Condition.java

/*
 * Copyright 2010-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */

package com.amazonaws.services.dynamodbv2.model;

import java.io.Serializable;

/**
 * <p>
 * Represents the selection criteria for a <i>Query</i> or <i>Scan</i>
 * operation:
 * </p>
 * <ul>
 * <li>
 * <p>
 * For a <i>Query</i> operation, <i>Condition</i> is used for specifying the
 * <i>KeyConditions</i> to use when querying a table or an index. For
 * <i>KeyConditions</i>, only the following comparison operators are supported:
 * </p>
 * <p>
 * <code>EQ | LE | LT | GE | GT | BEGINS_WITH | BETWEEN</code>
 * </p>
 * <p>
 * <i>Condition</i> is also used in a <i>QueryFilter</i>, which evaluates the
 * query results and returns only the desired values.
 * </p>
 * </li>
 * <li>
 * <p>
 * For a <i>Scan</i> operation, <i>Condition</i> is used in a <i>ScanFilter</i>,
 * which evaluates the scan results and returns only the desired values.
 * </p>
 * </li>
 * </ul>
 */
public class Condition implements Serializable {
    /**
     * <p>
     * One or more values to evaluate against the supplied attribute. The number
     * of values in the list depends on the <i>ComparisonOperator</i> being
     * used.
     * </p>
     * <p>
     * For type Number, value comparisons are numeric.
     * </p>
     * <p>
     * String value comparisons for greater than, equals, or less than are based
     * on ASCII character code values. For example, <code>a</code> is greater
     * than <code>A</code>, and <code>a</code> is greater than <code>B</code>.
     * For a list of code values, see <a
     * href="http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     * >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters</a>.
     * </p>
     * <p>
     * For Binary, DynamoDB treats each byte of the binary data as unsigned when
     * it compares binary values.
     * </p>
     */
    private java.util.List<AttributeValue> attributeValueList;

    /**
     * <p>
     * A comparator for evaluating attributes. For example, equals, greater
     * than, less than, etc.
     * </p>
     * <p>
     * The following comparison operators are available:
     * </p>
     * <p>
     * <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     * </p>
     * <p>
     * The following are descriptions of each comparison operator.
     * </p>
     * <ul>
     * <li>
     * <p>
     * <code>EQ</code> : Equal. <code>EQ</code> is supported for all datatypes,
     * including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, Binary, String Set, Number Set, or Binary
     * Set. If an item contains an <i>AttributeValue</i> element of a different
     * type than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     * Also, <code>{"N":"6"}</code> does not equal
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NE</code> : Not equal. <code>NE</code> is supported for all
     * datatypes, including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, Binary, String Set, Number Set, or Binary Set. If an
     * item contains an <i>AttributeValue</i> of a different type than the one
     * provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not equal <code>{"NS":["6", "2", "1"]}</code>
     * .
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LE</code> : Less than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LT</code> : Less than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, or Binary (not a set type). If an item contains an
     * <i>AttributeValue</i> element of a different type than the one provided
     * in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GE</code> : Greater than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GT</code> : Greater than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NOT_NULL</code> : The attribute exists. <code>NOT_NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the existence of an attribute, not its data type.
     * If the data type of attribute "<code>a</code>" is null, and you evaluate
     * it using <code>NOT_NULL</code>, the result is a Boolean <i>true</i>. This
     * result is because the attribute "<code>a</code>" exists; its data type is
     * not relevant to the <code>NOT_NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>NULL</code> : The attribute does not exist. <code>NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the nonexistence of an attribute, not its data
     * type. If the data type of attribute "<code>a</code>" is null, and you
     * evaluate it using <code>NULL</code>, the result is a Boolean
     * <i>false</i>. This is because the attribute "<code>a</code>" exists; its
     * data type is not relevant to the <code>NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>CONTAINS</code> : Checks for a subsequence, or value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is of type String, then the operator checks
     * for a substring match. If the target attribute of the comparison is of
     * type Binary, then the operator looks for a subsequence of the target that
     * matches the input. If the target attribute of the comparison is a set ("
     * <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then the
     * operator evaluates to true if it finds an exact match with any member of
     * the set.
     * </p>
     * <p>
     * CONTAINS is supported for lists: When evaluating "
     * <code>a CONTAINS b</code>", "<code>a</code>" can be a list; however, "
     * <code>b</code>" cannot be a set, a map, or a list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>NOT_CONTAINS</code> : Checks for absence of a subsequence, or
     * absence of a value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is a String, then the operator checks for the
     * absence of a substring match. If the target attribute of the comparison
     * is Binary, then the operator checks for the absence of a subsequence of
     * the target that matches the input. If the target attribute of the
     * comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     * <code>BS</code>"), then the operator evaluates to true if it <i>does
     * not</i> find an exact match with any member of the set.
     * </p>
     * <p>
     * NOT_CONTAINS is supported for lists: When evaluating "
     * <code>a NOT CONTAINS b</code>", "<code>a</code>
     * " can be a list; however, "<code>b</code>" cannot be a set, a map, or a
     * list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BEGINS_WITH</code> : Checks for a prefix.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String or Binary (not a Number or a set type). The target attribute
     * of the comparison must be of type String or Binary (not a Number or a set
     * type).
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>IN</code> : Checks for matching elements within two sets.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain one or more <i>AttributeValue</i>
     * elements of type String, Number, or Binary (not a set type). These
     * attributes are compared against an existing set type attribute of an
     * item. If any elements of the input set are present in the item attribute,
     * the expression evaluates to true.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BETWEEN</code> : Greater than or equal to the first value, and less
     * than or equal to the second value.
     * </p>
     * <p>
     * <i>AttributeValueList</i> must contain two <i>AttributeValue</i> elements
     * of the same type, either String, Number, or Binary (not a set type). A
     * target attribute matches if the target value is greater than, or equal
     * to, the first element and less than, or equal to, the second element. If
     * an item contains an <i>AttributeValue</i> element of a different type
     * than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not compare to
     * <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>
     * </p>
     * </li>
     * </ul>
     * <p>
     * For usage examples of <i>AttributeValueList</i> and
     * <i>ComparisonOperator</i>, see <a href=
     * "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     * >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB Developer
     * Guide</i>.
     * </p>
     * <p>
     * <b>Constraints:</b><br/>
     * <b>Allowed Values: </b>EQ, NE, IN, LE, LT, GE, GT, BETWEEN, NOT_NULL,
     * NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH
     */
    private String comparisonOperator;

    /**
     * <p>
     * One or more values to evaluate against the supplied attribute. The number
     * of values in the list depends on the <i>ComparisonOperator</i> being
     * used.
     * </p>
     * <p>
     * For type Number, value comparisons are numeric.
     * </p>
     * <p>
     * String value comparisons for greater than, equals, or less than are based
     * on ASCII character code values. For example, <code>a</code> is greater
     * than <code>A</code>, and <code>a</code> is greater than <code>B</code>.
     * For a list of code values, see <a
     * href="http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     * >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters</a>.
     * </p>
     * <p>
     * For Binary, DynamoDB treats each byte of the binary data as unsigned when
     * it compares binary values.
     * </p>
     *
     * @return <p>
     *         One or more values to evaluate against the supplied attribute.
     *         The number of values in the list depends on the
     *         <i>ComparisonOperator</i> being used.
     *         </p>
     *         <p>
     *         For type Number, value comparisons are numeric.
     *         </p>
     *         <p>
     *         String value comparisons for greater than, equals, or less than
     *         are based on ASCII character code values. For example,
     *         <code>a</code> is greater than <code>A</code>, and <code>a</code>
     *         is greater than <code>B</code>. For a list of code values, see <a
     *         href
     *         ="http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     *         >http
     *         ://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters</a>.
     *         </p>
     *         <p>
     *         For Binary, DynamoDB treats each byte of the binary data as
     *         unsigned when it compares binary values.
     *         </p>
     */
    public java.util.List<AttributeValue> getAttributeValueList() {
        return attributeValueList;
    }

    /**
     * <p>
     * One or more values to evaluate against the supplied attribute. The number
     * of values in the list depends on the <i>ComparisonOperator</i> being
     * used.
     * </p>
     * <p>
     * For type Number, value comparisons are numeric.
     * </p>
     * <p>
     * String value comparisons for greater than, equals, or less than are based
     * on ASCII character code values. For example, <code>a</code> is greater
     * than <code>A</code>, and <code>a</code> is greater than <code>B</code>.
     * For a list of code values, see <a
     * href="http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     * >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters</a>.
     * </p>
     * <p>
     * For Binary, DynamoDB treats each byte of the binary data as unsigned when
     * it compares binary values.
     * </p>
     *
     * @param attributeValueList <p>
     *            One or more values to evaluate against the supplied attribute.
     *            The number of values in the list depends on the
     *            <i>ComparisonOperator</i> being used.
     *            </p>
     *            <p>
     *            For type Number, value comparisons are numeric.
     *            </p>
     *            <p>
     *            String value comparisons for greater than, equals, or less
     *            than are based on ASCII character code values. For example,
     *            <code>a</code> is greater than <code>A</code>, and
     *            <code>a</code> is greater than <code>B</code>. For a list of
     *            code values, see <a href=
     *            "http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     *            >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
     *            </a>.
     *            </p>
     *            <p>
     *            For Binary, DynamoDB treats each byte of the binary data as
     *            unsigned when it compares binary values.
     *            </p>
     */
    public void setAttributeValueList(java.util.Collection<AttributeValue> attributeValueList) {
        if (attributeValueList == null) {
            this.attributeValueList = null;
            return;
        }

        this.attributeValueList = new java.util.ArrayList<AttributeValue>(attributeValueList);
    }

    /**
     * <p>
     * One or more values to evaluate against the supplied attribute. The number
     * of values in the list depends on the <i>ComparisonOperator</i> being
     * used.
     * </p>
     * <p>
     * For type Number, value comparisons are numeric.
     * </p>
     * <p>
     * String value comparisons for greater than, equals, or less than are based
     * on ASCII character code values. For example, <code>a</code> is greater
     * than <code>A</code>, and <code>a</code> is greater than <code>B</code>.
     * For a list of code values, see <a
     * href="http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     * >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters</a>.
     * </p>
     * <p>
     * For Binary, DynamoDB treats each byte of the binary data as unsigned when
     * it compares binary values.
     * </p>
     * <p>
     * Returns a reference to this object so that method calls can be chained
     * together.
     *
     * @param attributeValueList <p>
     *            One or more values to evaluate against the supplied attribute.
     *            The number of values in the list depends on the
     *            <i>ComparisonOperator</i> being used.
     *            </p>
     *            <p>
     *            For type Number, value comparisons are numeric.
     *            </p>
     *            <p>
     *            String value comparisons for greater than, equals, or less
     *            than are based on ASCII character code values. For example,
     *            <code>a</code> is greater than <code>A</code>, and
     *            <code>a</code> is greater than <code>B</code>. For a list of
     *            code values, see <a href=
     *            "http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     *            >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
     *            </a>.
     *            </p>
     *            <p>
     *            For Binary, DynamoDB treats each byte of the binary data as
     *            unsigned when it compares binary values.
     *            </p>
     * @return A reference to this updated object so that method calls can be
     *         chained together.
     */
    public Condition withAttributeValueList(AttributeValue... attributeValueList) {
        if (getAttributeValueList() == null) {
            this.attributeValueList = new java.util.ArrayList<AttributeValue>(
                    attributeValueList.length);
        }
        for (AttributeValue value : attributeValueList) {
            this.attributeValueList.add(value);
        }
        return this;
    }

    /**
     * <p>
     * One or more values to evaluate against the supplied attribute. The number
     * of values in the list depends on the <i>ComparisonOperator</i> being
     * used.
     * </p>
     * <p>
     * For type Number, value comparisons are numeric.
     * </p>
     * <p>
     * String value comparisons for greater than, equals, or less than are based
     * on ASCII character code values. For example, <code>a</code> is greater
     * than <code>A</code>, and <code>a</code> is greater than <code>B</code>.
     * For a list of code values, see <a
     * href="http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     * >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters</a>.
     * </p>
     * <p>
     * For Binary, DynamoDB treats each byte of the binary data as unsigned when
     * it compares binary values.
     * </p>
     * <p>
     * Returns a reference to this object so that method calls can be chained
     * together.
     *
     * @param attributeValueList <p>
     *            One or more values to evaluate against the supplied attribute.
     *            The number of values in the list depends on the
     *            <i>ComparisonOperator</i> being used.
     *            </p>
     *            <p>
     *            For type Number, value comparisons are numeric.
     *            </p>
     *            <p>
     *            String value comparisons for greater than, equals, or less
     *            than are based on ASCII character code values. For example,
     *            <code>a</code> is greater than <code>A</code>, and
     *            <code>a</code> is greater than <code>B</code>. For a list of
     *            code values, see <a href=
     *            "http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters"
     *            >http://en.wikipedia.org/wiki/ASCII#ASCII_printable_characters
     *            </a>.
     *            </p>
     *            <p>
     *            For Binary, DynamoDB treats each byte of the binary data as
     *            unsigned when it compares binary values.
     *            </p>
     * @return A reference to this updated object so that method calls can be
     *         chained together.
     */
    public Condition withAttributeValueList(java.util.Collection<AttributeValue> attributeValueList) {
        setAttributeValueList(attributeValueList);
        return this;
    }

    /**
     * <p>
     * A comparator for evaluating attributes. For example, equals, greater
     * than, less than, etc.
     * </p>
     * <p>
     * The following comparison operators are available:
     * </p>
     * <p>
     * <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     * </p>
     * <p>
     * The following are descriptions of each comparison operator.
     * </p>
     * <ul>
     * <li>
     * <p>
     * <code>EQ</code> : Equal. <code>EQ</code> is supported for all datatypes,
     * including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, Binary, String Set, Number Set, or Binary
     * Set. If an item contains an <i>AttributeValue</i> element of a different
     * type than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     * Also, <code>{"N":"6"}</code> does not equal
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NE</code> : Not equal. <code>NE</code> is supported for all
     * datatypes, including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, Binary, String Set, Number Set, or Binary Set. If an
     * item contains an <i>AttributeValue</i> of a different type than the one
     * provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not equal <code>{"NS":["6", "2", "1"]}</code>
     * .
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LE</code> : Less than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LT</code> : Less than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, or Binary (not a set type). If an item contains an
     * <i>AttributeValue</i> element of a different type than the one provided
     * in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GE</code> : Greater than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GT</code> : Greater than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NOT_NULL</code> : The attribute exists. <code>NOT_NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the existence of an attribute, not its data type.
     * If the data type of attribute "<code>a</code>" is null, and you evaluate
     * it using <code>NOT_NULL</code>, the result is a Boolean <i>true</i>. This
     * result is because the attribute "<code>a</code>" exists; its data type is
     * not relevant to the <code>NOT_NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>NULL</code> : The attribute does not exist. <code>NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the nonexistence of an attribute, not its data
     * type. If the data type of attribute "<code>a</code>" is null, and you
     * evaluate it using <code>NULL</code>, the result is a Boolean
     * <i>false</i>. This is because the attribute "<code>a</code>" exists; its
     * data type is not relevant to the <code>NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>CONTAINS</code> : Checks for a subsequence, or value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is of type String, then the operator checks
     * for a substring match. If the target attribute of the comparison is of
     * type Binary, then the operator looks for a subsequence of the target that
     * matches the input. If the target attribute of the comparison is a set ("
     * <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then the
     * operator evaluates to true if it finds an exact match with any member of
     * the set.
     * </p>
     * <p>
     * CONTAINS is supported for lists: When evaluating "
     * <code>a CONTAINS b</code>", "<code>a</code>" can be a list; however, "
     * <code>b</code>" cannot be a set, a map, or a list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>NOT_CONTAINS</code> : Checks for absence of a subsequence, or
     * absence of a value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is a String, then the operator checks for the
     * absence of a substring match. If the target attribute of the comparison
     * is Binary, then the operator checks for the absence of a subsequence of
     * the target that matches the input. If the target attribute of the
     * comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     * <code>BS</code>"), then the operator evaluates to true if it <i>does
     * not</i> find an exact match with any member of the set.
     * </p>
     * <p>
     * NOT_CONTAINS is supported for lists: When evaluating "
     * <code>a NOT CONTAINS b</code>", "<code>a</code>
     * " can be a list; however, "<code>b</code>" cannot be a set, a map, or a
     * list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BEGINS_WITH</code> : Checks for a prefix.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String or Binary (not a Number or a set type). The target attribute
     * of the comparison must be of type String or Binary (not a Number or a set
     * type).
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>IN</code> : Checks for matching elements within two sets.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain one or more <i>AttributeValue</i>
     * elements of type String, Number, or Binary (not a set type). These
     * attributes are compared against an existing set type attribute of an
     * item. If any elements of the input set are present in the item attribute,
     * the expression evaluates to true.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BETWEEN</code> : Greater than or equal to the first value, and less
     * than or equal to the second value.
     * </p>
     * <p>
     * <i>AttributeValueList</i> must contain two <i>AttributeValue</i> elements
     * of the same type, either String, Number, or Binary (not a set type). A
     * target attribute matches if the target value is greater than, or equal
     * to, the first element and less than, or equal to, the second element. If
     * an item contains an <i>AttributeValue</i> element of a different type
     * than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not compare to
     * <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>
     * </p>
     * </li>
     * </ul>
     * <p>
     * For usage examples of <i>AttributeValueList</i> and
     * <i>ComparisonOperator</i>, see <a href=
     * "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     * >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB Developer
     * Guide</i>.
     * </p>
     * <p>
     * <b>Constraints:</b><br/>
     * <b>Allowed Values: </b>EQ, NE, IN, LE, LT, GE, GT, BETWEEN, NOT_NULL,
     * NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH
     *
     * @return <p>
     *         A comparator for evaluating attributes. For example, equals,
     *         greater than, less than, etc.
     *         </p>
     *         <p>
     *         The following comparison operators are available:
     *         </p>
     *         <p>
     *         <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     *         </p>
     *         <p>
     *         The following are descriptions of each comparison operator.
     *         </p>
     *         <ul>
     *         <li>
     *         <p>
     *         <code>EQ</code> : Equal. <code>EQ</code> is supported for all
     *         datatypes, including lists and maps.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> element of type String, Number, Binary,
     *         String Set, Number Set, or Binary Set. If an item contains an
     *         <i>AttributeValue</i> element of a different type than the one
     *         provided in the request, the value does not match. For example,
     *         <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     *         Also, <code>{"N":"6"}</code> does not equal
     *         <code>{"NS":["6", "2", "1"]}</code>.
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>NE</code> : Not equal. <code>NE</code> is supported for all
     *         datatypes, including lists and maps.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> of type String, Number, Binary, String Set,
     *         Number Set, or Binary Set. If an item contains an
     *         <i>AttributeValue</i> of a different type than the one provided
     *         in the request, the value does not match. For example,
     *         <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     *         Also, <code>{"N":"6"}</code> does not equal
     *         <code>{"NS":["6", "2", "1"]}</code>.
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>LE</code> : Less than or equal.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> element of type String, Number, or Binary
     *         (not a set type). If an item contains an <i>AttributeValue</i>
     *         element of a different type than the one provided in the request,
     *         the value does not match. For example, <code>{"S":"6"}</code>
     *         does not equal <code>{"N":"6"}</code>. Also,
     *         <code>{"N":"6"}</code> does not compare to
     *         <code>{"NS":["6", "2", "1"]}</code>.
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>LT</code> : Less than.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> of type String, Number, or Binary (not a
     *         set type). If an item contains an <i>AttributeValue</i> element
     *         of a different type than the one provided in the request, the
     *         value does not match. For example, <code>{"S":"6"}</code> does
     *         not equal <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code>
     *         does not compare to <code>{"NS":["6", "2", "1"]}</code>.
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>GE</code> : Greater than or equal.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> element of type String, Number, or Binary
     *         (not a set type). If an item contains an <i>AttributeValue</i>
     *         element of a different type than the one provided in the request,
     *         the value does not match. For example, <code>{"S":"6"}</code>
     *         does not equal <code>{"N":"6"}</code>. Also,
     *         <code>{"N":"6"}</code> does not compare to
     *         <code>{"NS":["6", "2", "1"]}</code>.
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>GT</code> : Greater than.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> element of type String, Number, or Binary
     *         (not a set type). If an item contains an <i>AttributeValue</i>
     *         element of a different type than the one provided in the request,
     *         the value does not match. For example, <code>{"S":"6"}</code>
     *         does not equal <code>{"N":"6"}</code>. Also,
     *         <code>{"N":"6"}</code> does not compare to
     *         <code>{"NS":["6", "2", "1"]}</code>.
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>NOT_NULL</code> : The attribute exists.
     *         <code>NOT_NULL</code> is supported for all datatypes, including
     *         lists and maps.
     *         </p>
     *         <note>
     *         <p>
     *         This operator tests for the existence of an attribute, not its
     *         data type. If the data type of attribute "<code>a</code>" is
     *         null, and you evaluate it using <code>NOT_NULL</code>, the result
     *         is a Boolean <i>true</i>. This result is because the attribute "
     *         <code>a</code>" exists; its data type is not relevant to the
     *         <code>NOT_NULL</code> comparison operator.
     *         </p>
     *         </note></li>
     *         <li>
     *         <p>
     *         <code>NULL</code> : The attribute does not exist.
     *         <code>NULL</code> is supported for all datatypes, including lists
     *         and maps.
     *         </p>
     *         <note>
     *         <p>
     *         This operator tests for the nonexistence of an attribute, not its
     *         data type. If the data type of attribute "<code>a</code>" is
     *         null, and you evaluate it using <code>NULL</code>, the result is
     *         a Boolean <i>false</i>. This is because the attribute "
     *         <code>a</code>" exists; its data type is not relevant to the
     *         <code>NULL</code> comparison operator.
     *         </p>
     *         </note></li>
     *         <li>
     *         <p>
     *         <code>CONTAINS</code> : Checks for a subsequence, or value in a
     *         set.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> element of type String, Number, or Binary
     *         (not a set type). If the target attribute of the comparison is of
     *         type String, then the operator checks for a substring match. If
     *         the target attribute of the comparison is of type Binary, then
     *         the operator looks for a subsequence of the target that matches
     *         the input. If the target attribute of the comparison is a set ("
     *         <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then
     *         the operator evaluates to true if it finds an exact match with
     *         any member of the set.
     *         </p>
     *         <p>
     *         CONTAINS is supported for lists: When evaluating "
     *         <code>a CONTAINS b</code>", "<code>a</code>
     *         " can be a list; however, "<code>b</code>" cannot be a set, a
     *         map, or a list.
     *         </p>
     *         </li>
     *         <li>
     *         <p>
     *         <code>NOT_CONTAINS</code> : Checks for absence of a subsequence,
     *         or absence of a value in a set.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> element of type String, Number, or Binary
     *         (not a set type). If the target attribute of the comparison is a
     *         String, then the operator checks for the absence of a substring
     *         match. If the target attribute of the comparison is Binary, then
     *         the operator checks for the absence of a subsequence of the
     *         target that matches the input. If the target attribute of the
     *         comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     *         <code>BS</code>"), then the operator evaluates to true if it
     *         <i>does not</i> find an exact match with any member of the set.
     *         </p>
     *         <p>
     *         NOT_CONTAINS is supported for lists: When evaluating "
     *         <code>a NOT CONTAINS b</code>", "<code>a</code>
     *         " can be a list; however, "<code>b</code>" cannot be a set, a
     *         map, or a list.
     *         </p>
     *         </li>
     *         <li>
     *         <p>
     *         <code>BEGINS_WITH</code> : Checks for a prefix.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain only one
     *         <i>AttributeValue</i> of type String or Binary (not a Number or a
     *         set type). The target attribute of the comparison must be of type
     *         String or Binary (not a Number or a set type).
     *         </p>
     *         <p/></li>
     *         <li>
     *         <p>
     *         <code>IN</code> : Checks for matching elements within two sets.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> can contain one or more
     *         <i>AttributeValue</i> elements of type String, Number, or Binary
     *         (not a set type). These attributes are compared against an
     *         existing set type attribute of an item. If any elements of the
     *         input set are present in the item attribute, the expression
     *         evaluates to true.
     *         </p>
     *         </li>
     *         <li>
     *         <p>
     *         <code>BETWEEN</code> : Greater than or equal to the first value,
     *         and less than or equal to the second value.
     *         </p>
     *         <p>
     *         <i>AttributeValueList</i> must contain two <i>AttributeValue</i>
     *         elements of the same type, either String, Number, or Binary (not
     *         a set type). A target attribute matches if the target value is
     *         greater than, or equal to, the first element and less than, or
     *         equal to, the second element. If an item contains an
     *         <i>AttributeValue</i> element of a different type than the one
     *         provided in the request, the value does not match. For example,
     *         <code>{"S":"6"}</code> does not compare to <code>{"N":"6"}</code>
     *         . Also, <code>{"N":"6"}</code> does not compare to
     *         <code>{"NS":["6", "2", "1"]}</code>
     *         </p>
     *         </li>
     *         </ul>
     *         <p>
     *         For usage examples of <i>AttributeValueList</i> and
     *         <i>ComparisonOperator</i>, see <a href=
     *         "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     *         >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB
     *         Developer Guide</i>.
     *         </p>
     * @see ComparisonOperator
     */
    public String getComparisonOperator() {
        return comparisonOperator;
    }

    /**
     * <p>
     * A comparator for evaluating attributes. For example, equals, greater
     * than, less than, etc.
     * </p>
     * <p>
     * The following comparison operators are available:
     * </p>
     * <p>
     * <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     * </p>
     * <p>
     * The following are descriptions of each comparison operator.
     * </p>
     * <ul>
     * <li>
     * <p>
     * <code>EQ</code> : Equal. <code>EQ</code> is supported for all datatypes,
     * including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, Binary, String Set, Number Set, or Binary
     * Set. If an item contains an <i>AttributeValue</i> element of a different
     * type than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     * Also, <code>{"N":"6"}</code> does not equal
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NE</code> : Not equal. <code>NE</code> is supported for all
     * datatypes, including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, Binary, String Set, Number Set, or Binary Set. If an
     * item contains an <i>AttributeValue</i> of a different type than the one
     * provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not equal <code>{"NS":["6", "2", "1"]}</code>
     * .
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LE</code> : Less than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LT</code> : Less than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, or Binary (not a set type). If an item contains an
     * <i>AttributeValue</i> element of a different type than the one provided
     * in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GE</code> : Greater than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GT</code> : Greater than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NOT_NULL</code> : The attribute exists. <code>NOT_NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the existence of an attribute, not its data type.
     * If the data type of attribute "<code>a</code>" is null, and you evaluate
     * it using <code>NOT_NULL</code>, the result is a Boolean <i>true</i>. This
     * result is because the attribute "<code>a</code>" exists; its data type is
     * not relevant to the <code>NOT_NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>NULL</code> : The attribute does not exist. <code>NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the nonexistence of an attribute, not its data
     * type. If the data type of attribute "<code>a</code>" is null, and you
     * evaluate it using <code>NULL</code>, the result is a Boolean
     * <i>false</i>. This is because the attribute "<code>a</code>" exists; its
     * data type is not relevant to the <code>NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>CONTAINS</code> : Checks for a subsequence, or value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is of type String, then the operator checks
     * for a substring match. If the target attribute of the comparison is of
     * type Binary, then the operator looks for a subsequence of the target that
     * matches the input. If the target attribute of the comparison is a set ("
     * <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then the
     * operator evaluates to true if it finds an exact match with any member of
     * the set.
     * </p>
     * <p>
     * CONTAINS is supported for lists: When evaluating "
     * <code>a CONTAINS b</code>", "<code>a</code>" can be a list; however, "
     * <code>b</code>" cannot be a set, a map, or a list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>NOT_CONTAINS</code> : Checks for absence of a subsequence, or
     * absence of a value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is a String, then the operator checks for the
     * absence of a substring match. If the target attribute of the comparison
     * is Binary, then the operator checks for the absence of a subsequence of
     * the target that matches the input. If the target attribute of the
     * comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     * <code>BS</code>"), then the operator evaluates to true if it <i>does
     * not</i> find an exact match with any member of the set.
     * </p>
     * <p>
     * NOT_CONTAINS is supported for lists: When evaluating "
     * <code>a NOT CONTAINS b</code>", "<code>a</code>
     * " can be a list; however, "<code>b</code>" cannot be a set, a map, or a
     * list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BEGINS_WITH</code> : Checks for a prefix.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String or Binary (not a Number or a set type). The target attribute
     * of the comparison must be of type String or Binary (not a Number or a set
     * type).
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>IN</code> : Checks for matching elements within two sets.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain one or more <i>AttributeValue</i>
     * elements of type String, Number, or Binary (not a set type). These
     * attributes are compared against an existing set type attribute of an
     * item. If any elements of the input set are present in the item attribute,
     * the expression evaluates to true.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BETWEEN</code> : Greater than or equal to the first value, and less
     * than or equal to the second value.
     * </p>
     * <p>
     * <i>AttributeValueList</i> must contain two <i>AttributeValue</i> elements
     * of the same type, either String, Number, or Binary (not a set type). A
     * target attribute matches if the target value is greater than, or equal
     * to, the first element and less than, or equal to, the second element. If
     * an item contains an <i>AttributeValue</i> element of a different type
     * than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not compare to
     * <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>
     * </p>
     * </li>
     * </ul>
     * <p>
     * For usage examples of <i>AttributeValueList</i> and
     * <i>ComparisonOperator</i>, see <a href=
     * "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     * >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB Developer
     * Guide</i>.
     * </p>
     * <p>
     * <b>Constraints:</b><br/>
     * <b>Allowed Values: </b>EQ, NE, IN, LE, LT, GE, GT, BETWEEN, NOT_NULL,
     * NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH
     *
     * @param comparisonOperator <p>
     *            A comparator for evaluating attributes. For example, equals,
     *            greater than, less than, etc.
     *            </p>
     *            <p>
     *            The following comparison operators are available:
     *            </p>
     *            <p>
     *            <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     *            </p>
     *            <p>
     *            The following are descriptions of each comparison operator.
     *            </p>
     *            <ul>
     *            <li>
     *            <p>
     *            <code>EQ</code> : Equal. <code>EQ</code> is supported for all
     *            datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, Binary,
     *            String Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NE</code> : Not equal. <code>NE</code> is supported for
     *            all datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, Binary, String
     *            Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LE</code> : Less than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LT</code> : Less than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, or Binary (not a
     *            set type). If an item contains an <i>AttributeValue</i>
     *            element of a different type than the one provided in the
     *            request, the value does not match. For example,
     *            <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     *            Also, <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GE</code> : Greater than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GT</code> : Greater than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NOT_NULL</code> : The attribute exists.
     *            <code>NOT_NULL</code> is supported for all datatypes,
     *            including lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the existence of an attribute, not its
     *            data type. If the data type of attribute "<code>a</code>" is
     *            null, and you evaluate it using <code>NOT_NULL</code>, the
     *            result is a Boolean <i>true</i>. This result is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NOT_NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>NULL</code> : The attribute does not exist.
     *            <code>NULL</code> is supported for all datatypes, including
     *            lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the nonexistence of an attribute, not
     *            its data type. If the data type of attribute "<code>a</code>"
     *            is null, and you evaluate it using <code>NULL</code>, the
     *            result is a Boolean <i>false</i>. This is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>CONTAINS</code> : Checks for a subsequence, or value in
     *            a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is of type String, then the operator checks for a
     *            substring match. If the target attribute of the comparison is
     *            of type Binary, then the operator looks for a subsequence of
     *            the target that matches the input. If the target attribute of
     *            the comparison is a set ("<code>SS</code>", "<code>NS</code>
     *            ", or "<code>BS</code>"), then the operator evaluates to true
     *            if it finds an exact match with any member of the set.
     *            </p>
     *            <p>
     *            CONTAINS is supported for lists: When evaluating "
     *            <code>a CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>NOT_CONTAINS</code> : Checks for absence of a
     *            subsequence, or absence of a value in a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is a String, then the operator checks for the
     *            absence of a substring match. If the target attribute of the
     *            comparison is Binary, then the operator checks for the absence
     *            of a subsequence of the target that matches the input. If the
     *            target attribute of the comparison is a set ("<code>SS</code>
     *            ", "<code>NS</code>", or "<code>BS</code>"), then the operator
     *            evaluates to true if it <i>does not</i> find an exact match
     *            with any member of the set.
     *            </p>
     *            <p>
     *            NOT_CONTAINS is supported for lists: When evaluating "
     *            <code>a NOT CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BEGINS_WITH</code> : Checks for a prefix.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String or Binary (not a Number
     *            or a set type). The target attribute of the comparison must be
     *            of type String or Binary (not a Number or a set type).
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>IN</code> : Checks for matching elements within two
     *            sets.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain one or more
     *            <i>AttributeValue</i> elements of type String, Number, or
     *            Binary (not a set type). These attributes are compared against
     *            an existing set type attribute of an item. If any elements of
     *            the input set are present in the item attribute, the
     *            expression evaluates to true.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BETWEEN</code> : Greater than or equal to the first
     *            value, and less than or equal to the second value.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> must contain two
     *            <i>AttributeValue</i> elements of the same type, either
     *            String, Number, or Binary (not a set type). A target attribute
     *            matches if the target value is greater than, or equal to, the
     *            first element and less than, or equal to, the second element.
     *            If an item contains an <i>AttributeValue</i> element of a
     *            different type than the one provided in the request, the value
     *            does not match. For example, <code>{"S":"6"}</code> does not
     *            compare to <code>{"N":"6"}</code>. Also,
     *            <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>
     *            </p>
     *            </li>
     *            </ul>
     *            <p>
     *            For usage examples of <i>AttributeValueList</i> and
     *            <i>ComparisonOperator</i>, see <a href=
     *            "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     *            >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB
     *            Developer Guide</i>.
     *            </p>
     * @see ComparisonOperator
     */
    public void setComparisonOperator(String comparisonOperator) {
        this.comparisonOperator = comparisonOperator;
    }

    /**
     * <p>
     * A comparator for evaluating attributes. For example, equals, greater
     * than, less than, etc.
     * </p>
     * <p>
     * The following comparison operators are available:
     * </p>
     * <p>
     * <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     * </p>
     * <p>
     * The following are descriptions of each comparison operator.
     * </p>
     * <ul>
     * <li>
     * <p>
     * <code>EQ</code> : Equal. <code>EQ</code> is supported for all datatypes,
     * including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, Binary, String Set, Number Set, or Binary
     * Set. If an item contains an <i>AttributeValue</i> element of a different
     * type than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     * Also, <code>{"N":"6"}</code> does not equal
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NE</code> : Not equal. <code>NE</code> is supported for all
     * datatypes, including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, Binary, String Set, Number Set, or Binary Set. If an
     * item contains an <i>AttributeValue</i> of a different type than the one
     * provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not equal <code>{"NS":["6", "2", "1"]}</code>
     * .
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LE</code> : Less than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LT</code> : Less than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, or Binary (not a set type). If an item contains an
     * <i>AttributeValue</i> element of a different type than the one provided
     * in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GE</code> : Greater than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GT</code> : Greater than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NOT_NULL</code> : The attribute exists. <code>NOT_NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the existence of an attribute, not its data type.
     * If the data type of attribute "<code>a</code>" is null, and you evaluate
     * it using <code>NOT_NULL</code>, the result is a Boolean <i>true</i>. This
     * result is because the attribute "<code>a</code>" exists; its data type is
     * not relevant to the <code>NOT_NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>NULL</code> : The attribute does not exist. <code>NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the nonexistence of an attribute, not its data
     * type. If the data type of attribute "<code>a</code>" is null, and you
     * evaluate it using <code>NULL</code>, the result is a Boolean
     * <i>false</i>. This is because the attribute "<code>a</code>" exists; its
     * data type is not relevant to the <code>NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>CONTAINS</code> : Checks for a subsequence, or value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is of type String, then the operator checks
     * for a substring match. If the target attribute of the comparison is of
     * type Binary, then the operator looks for a subsequence of the target that
     * matches the input. If the target attribute of the comparison is a set ("
     * <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then the
     * operator evaluates to true if it finds an exact match with any member of
     * the set.
     * </p>
     * <p>
     * CONTAINS is supported for lists: When evaluating "
     * <code>a CONTAINS b</code>", "<code>a</code>" can be a list; however, "
     * <code>b</code>" cannot be a set, a map, or a list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>NOT_CONTAINS</code> : Checks for absence of a subsequence, or
     * absence of a value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is a String, then the operator checks for the
     * absence of a substring match. If the target attribute of the comparison
     * is Binary, then the operator checks for the absence of a subsequence of
     * the target that matches the input. If the target attribute of the
     * comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     * <code>BS</code>"), then the operator evaluates to true if it <i>does
     * not</i> find an exact match with any member of the set.
     * </p>
     * <p>
     * NOT_CONTAINS is supported for lists: When evaluating "
     * <code>a NOT CONTAINS b</code>", "<code>a</code>
     * " can be a list; however, "<code>b</code>" cannot be a set, a map, or a
     * list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BEGINS_WITH</code> : Checks for a prefix.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String or Binary (not a Number or a set type). The target attribute
     * of the comparison must be of type String or Binary (not a Number or a set
     * type).
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>IN</code> : Checks for matching elements within two sets.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain one or more <i>AttributeValue</i>
     * elements of type String, Number, or Binary (not a set type). These
     * attributes are compared against an existing set type attribute of an
     * item. If any elements of the input set are present in the item attribute,
     * the expression evaluates to true.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BETWEEN</code> : Greater than or equal to the first value, and less
     * than or equal to the second value.
     * </p>
     * <p>
     * <i>AttributeValueList</i> must contain two <i>AttributeValue</i> elements
     * of the same type, either String, Number, or Binary (not a set type). A
     * target attribute matches if the target value is greater than, or equal
     * to, the first element and less than, or equal to, the second element. If
     * an item contains an <i>AttributeValue</i> element of a different type
     * than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not compare to
     * <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>
     * </p>
     * </li>
     * </ul>
     * <p>
     * For usage examples of <i>AttributeValueList</i> and
     * <i>ComparisonOperator</i>, see <a href=
     * "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     * >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB Developer
     * Guide</i>.
     * </p>
     * <p>
     * Returns a reference to this object so that method calls can be chained
     * together.
     * <p>
     * <b>Constraints:</b><br/>
     * <b>Allowed Values: </b>EQ, NE, IN, LE, LT, GE, GT, BETWEEN, NOT_NULL,
     * NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH
     *
     * @param comparisonOperator <p>
     *            A comparator for evaluating attributes. For example, equals,
     *            greater than, less than, etc.
     *            </p>
     *            <p>
     *            The following comparison operators are available:
     *            </p>
     *            <p>
     *            <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     *            </p>
     *            <p>
     *            The following are descriptions of each comparison operator.
     *            </p>
     *            <ul>
     *            <li>
     *            <p>
     *            <code>EQ</code> : Equal. <code>EQ</code> is supported for all
     *            datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, Binary,
     *            String Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NE</code> : Not equal. <code>NE</code> is supported for
     *            all datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, Binary, String
     *            Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LE</code> : Less than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LT</code> : Less than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, or Binary (not a
     *            set type). If an item contains an <i>AttributeValue</i>
     *            element of a different type than the one provided in the
     *            request, the value does not match. For example,
     *            <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     *            Also, <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GE</code> : Greater than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GT</code> : Greater than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NOT_NULL</code> : The attribute exists.
     *            <code>NOT_NULL</code> is supported for all datatypes,
     *            including lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the existence of an attribute, not its
     *            data type. If the data type of attribute "<code>a</code>" is
     *            null, and you evaluate it using <code>NOT_NULL</code>, the
     *            result is a Boolean <i>true</i>. This result is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NOT_NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>NULL</code> : The attribute does not exist.
     *            <code>NULL</code> is supported for all datatypes, including
     *            lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the nonexistence of an attribute, not
     *            its data type. If the data type of attribute "<code>a</code>"
     *            is null, and you evaluate it using <code>NULL</code>, the
     *            result is a Boolean <i>false</i>. This is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>CONTAINS</code> : Checks for a subsequence, or value in
     *            a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is of type String, then the operator checks for a
     *            substring match. If the target attribute of the comparison is
     *            of type Binary, then the operator looks for a subsequence of
     *            the target that matches the input. If the target attribute of
     *            the comparison is a set ("<code>SS</code>", "<code>NS</code>
     *            ", or "<code>BS</code>"), then the operator evaluates to true
     *            if it finds an exact match with any member of the set.
     *            </p>
     *            <p>
     *            CONTAINS is supported for lists: When evaluating "
     *            <code>a CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>NOT_CONTAINS</code> : Checks for absence of a
     *            subsequence, or absence of a value in a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is a String, then the operator checks for the
     *            absence of a substring match. If the target attribute of the
     *            comparison is Binary, then the operator checks for the absence
     *            of a subsequence of the target that matches the input. If the
     *            target attribute of the comparison is a set ("<code>SS</code>
     *            ", "<code>NS</code>", or "<code>BS</code>"), then the operator
     *            evaluates to true if it <i>does not</i> find an exact match
     *            with any member of the set.
     *            </p>
     *            <p>
     *            NOT_CONTAINS is supported for lists: When evaluating "
     *            <code>a NOT CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BEGINS_WITH</code> : Checks for a prefix.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String or Binary (not a Number
     *            or a set type). The target attribute of the comparison must be
     *            of type String or Binary (not a Number or a set type).
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>IN</code> : Checks for matching elements within two
     *            sets.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain one or more
     *            <i>AttributeValue</i> elements of type String, Number, or
     *            Binary (not a set type). These attributes are compared against
     *            an existing set type attribute of an item. If any elements of
     *            the input set are present in the item attribute, the
     *            expression evaluates to true.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BETWEEN</code> : Greater than or equal to the first
     *            value, and less than or equal to the second value.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> must contain two
     *            <i>AttributeValue</i> elements of the same type, either
     *            String, Number, or Binary (not a set type). A target attribute
     *            matches if the target value is greater than, or equal to, the
     *            first element and less than, or equal to, the second element.
     *            If an item contains an <i>AttributeValue</i> element of a
     *            different type than the one provided in the request, the value
     *            does not match. For example, <code>{"S":"6"}</code> does not
     *            compare to <code>{"N":"6"}</code>. Also,
     *            <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>
     *            </p>
     *            </li>
     *            </ul>
     *            <p>
     *            For usage examples of <i>AttributeValueList</i> and
     *            <i>ComparisonOperator</i>, see <a href=
     *            "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     *            >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB
     *            Developer Guide</i>.
     *            </p>
     * @return A reference to this updated object so that method calls can be
     *         chained together.
     * @see ComparisonOperator
     */
    public Condition withComparisonOperator(String comparisonOperator) {
        this.comparisonOperator = comparisonOperator;
        return this;
    }

    /**
     * <p>
     * A comparator for evaluating attributes. For example, equals, greater
     * than, less than, etc.
     * </p>
     * <p>
     * The following comparison operators are available:
     * </p>
     * <p>
     * <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     * </p>
     * <p>
     * The following are descriptions of each comparison operator.
     * </p>
     * <ul>
     * <li>
     * <p>
     * <code>EQ</code> : Equal. <code>EQ</code> is supported for all datatypes,
     * including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, Binary, String Set, Number Set, or Binary
     * Set. If an item contains an <i>AttributeValue</i> element of a different
     * type than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     * Also, <code>{"N":"6"}</code> does not equal
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NE</code> : Not equal. <code>NE</code> is supported for all
     * datatypes, including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, Binary, String Set, Number Set, or Binary Set. If an
     * item contains an <i>AttributeValue</i> of a different type than the one
     * provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not equal <code>{"NS":["6", "2", "1"]}</code>
     * .
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LE</code> : Less than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LT</code> : Less than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, or Binary (not a set type). If an item contains an
     * <i>AttributeValue</i> element of a different type than the one provided
     * in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GE</code> : Greater than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GT</code> : Greater than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NOT_NULL</code> : The attribute exists. <code>NOT_NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the existence of an attribute, not its data type.
     * If the data type of attribute "<code>a</code>" is null, and you evaluate
     * it using <code>NOT_NULL</code>, the result is a Boolean <i>true</i>. This
     * result is because the attribute "<code>a</code>" exists; its data type is
     * not relevant to the <code>NOT_NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>NULL</code> : The attribute does not exist. <code>NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the nonexistence of an attribute, not its data
     * type. If the data type of attribute "<code>a</code>" is null, and you
     * evaluate it using <code>NULL</code>, the result is a Boolean
     * <i>false</i>. This is because the attribute "<code>a</code>" exists; its
     * data type is not relevant to the <code>NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>CONTAINS</code> : Checks for a subsequence, or value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is of type String, then the operator checks
     * for a substring match. If the target attribute of the comparison is of
     * type Binary, then the operator looks for a subsequence of the target that
     * matches the input. If the target attribute of the comparison is a set ("
     * <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then the
     * operator evaluates to true if it finds an exact match with any member of
     * the set.
     * </p>
     * <p>
     * CONTAINS is supported for lists: When evaluating "
     * <code>a CONTAINS b</code>", "<code>a</code>" can be a list; however, "
     * <code>b</code>" cannot be a set, a map, or a list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>NOT_CONTAINS</code> : Checks for absence of a subsequence, or
     * absence of a value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is a String, then the operator checks for the
     * absence of a substring match. If the target attribute of the comparison
     * is Binary, then the operator checks for the absence of a subsequence of
     * the target that matches the input. If the target attribute of the
     * comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     * <code>BS</code>"), then the operator evaluates to true if it <i>does
     * not</i> find an exact match with any member of the set.
     * </p>
     * <p>
     * NOT_CONTAINS is supported for lists: When evaluating "
     * <code>a NOT CONTAINS b</code>", "<code>a</code>
     * " can be a list; however, "<code>b</code>" cannot be a set, a map, or a
     * list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BEGINS_WITH</code> : Checks for a prefix.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String or Binary (not a Number or a set type). The target attribute
     * of the comparison must be of type String or Binary (not a Number or a set
     * type).
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>IN</code> : Checks for matching elements within two sets.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain one or more <i>AttributeValue</i>
     * elements of type String, Number, or Binary (not a set type). These
     * attributes are compared against an existing set type attribute of an
     * item. If any elements of the input set are present in the item attribute,
     * the expression evaluates to true.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BETWEEN</code> : Greater than or equal to the first value, and less
     * than or equal to the second value.
     * </p>
     * <p>
     * <i>AttributeValueList</i> must contain two <i>AttributeValue</i> elements
     * of the same type, either String, Number, or Binary (not a set type). A
     * target attribute matches if the target value is greater than, or equal
     * to, the first element and less than, or equal to, the second element. If
     * an item contains an <i>AttributeValue</i> element of a different type
     * than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not compare to
     * <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>
     * </p>
     * </li>
     * </ul>
     * <p>
     * For usage examples of <i>AttributeValueList</i> and
     * <i>ComparisonOperator</i>, see <a href=
     * "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     * >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB Developer
     * Guide</i>.
     * </p>
     * <p>
     * <b>Constraints:</b><br/>
     * <b>Allowed Values: </b>EQ, NE, IN, LE, LT, GE, GT, BETWEEN, NOT_NULL,
     * NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH
     *
     * @param comparisonOperator <p>
     *            A comparator for evaluating attributes. For example, equals,
     *            greater than, less than, etc.
     *            </p>
     *            <p>
     *            The following comparison operators are available:
     *            </p>
     *            <p>
     *            <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     *            </p>
     *            <p>
     *            The following are descriptions of each comparison operator.
     *            </p>
     *            <ul>
     *            <li>
     *            <p>
     *            <code>EQ</code> : Equal. <code>EQ</code> is supported for all
     *            datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, Binary,
     *            String Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NE</code> : Not equal. <code>NE</code> is supported for
     *            all datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, Binary, String
     *            Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LE</code> : Less than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LT</code> : Less than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, or Binary (not a
     *            set type). If an item contains an <i>AttributeValue</i>
     *            element of a different type than the one provided in the
     *            request, the value does not match. For example,
     *            <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     *            Also, <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GE</code> : Greater than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GT</code> : Greater than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NOT_NULL</code> : The attribute exists.
     *            <code>NOT_NULL</code> is supported for all datatypes,
     *            including lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the existence of an attribute, not its
     *            data type. If the data type of attribute "<code>a</code>" is
     *            null, and you evaluate it using <code>NOT_NULL</code>, the
     *            result is a Boolean <i>true</i>. This result is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NOT_NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>NULL</code> : The attribute does not exist.
     *            <code>NULL</code> is supported for all datatypes, including
     *            lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the nonexistence of an attribute, not
     *            its data type. If the data type of attribute "<code>a</code>"
     *            is null, and you evaluate it using <code>NULL</code>, the
     *            result is a Boolean <i>false</i>. This is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>CONTAINS</code> : Checks for a subsequence, or value in
     *            a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is of type String, then the operator checks for a
     *            substring match. If the target attribute of the comparison is
     *            of type Binary, then the operator looks for a subsequence of
     *            the target that matches the input. If the target attribute of
     *            the comparison is a set ("<code>SS</code>", "<code>NS</code>
     *            ", or "<code>BS</code>"), then the operator evaluates to true
     *            if it finds an exact match with any member of the set.
     *            </p>
     *            <p>
     *            CONTAINS is supported for lists: When evaluating "
     *            <code>a CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>NOT_CONTAINS</code> : Checks for absence of a
     *            subsequence, or absence of a value in a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is a String, then the operator checks for the
     *            absence of a substring match. If the target attribute of the
     *            comparison is Binary, then the operator checks for the absence
     *            of a subsequence of the target that matches the input. If the
     *            target attribute of the comparison is a set ("<code>SS</code>
     *            ", "<code>NS</code>", or "<code>BS</code>"), then the operator
     *            evaluates to true if it <i>does not</i> find an exact match
     *            with any member of the set.
     *            </p>
     *            <p>
     *            NOT_CONTAINS is supported for lists: When evaluating "
     *            <code>a NOT CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BEGINS_WITH</code> : Checks for a prefix.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String or Binary (not a Number
     *            or a set type). The target attribute of the comparison must be
     *            of type String or Binary (not a Number or a set type).
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>IN</code> : Checks for matching elements within two
     *            sets.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain one or more
     *            <i>AttributeValue</i> elements of type String, Number, or
     *            Binary (not a set type). These attributes are compared against
     *            an existing set type attribute of an item. If any elements of
     *            the input set are present in the item attribute, the
     *            expression evaluates to true.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BETWEEN</code> : Greater than or equal to the first
     *            value, and less than or equal to the second value.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> must contain two
     *            <i>AttributeValue</i> elements of the same type, either
     *            String, Number, or Binary (not a set type). A target attribute
     *            matches if the target value is greater than, or equal to, the
     *            first element and less than, or equal to, the second element.
     *            If an item contains an <i>AttributeValue</i> element of a
     *            different type than the one provided in the request, the value
     *            does not match. For example, <code>{"S":"6"}</code> does not
     *            compare to <code>{"N":"6"}</code>. Also,
     *            <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>
     *            </p>
     *            </li>
     *            </ul>
     *            <p>
     *            For usage examples of <i>AttributeValueList</i> and
     *            <i>ComparisonOperator</i>, see <a href=
     *            "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     *            >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB
     *            Developer Guide</i>.
     *            </p>
     * @see ComparisonOperator
     */
    public void setComparisonOperator(ComparisonOperator comparisonOperator) {
        this.comparisonOperator = comparisonOperator.toString();
    }

    /**
     * <p>
     * A comparator for evaluating attributes. For example, equals, greater
     * than, less than, etc.
     * </p>
     * <p>
     * The following comparison operators are available:
     * </p>
     * <p>
     * <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     * </p>
     * <p>
     * The following are descriptions of each comparison operator.
     * </p>
     * <ul>
     * <li>
     * <p>
     * <code>EQ</code> : Equal. <code>EQ</code> is supported for all datatypes,
     * including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, Binary, String Set, Number Set, or Binary
     * Set. If an item contains an <i>AttributeValue</i> element of a different
     * type than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     * Also, <code>{"N":"6"}</code> does not equal
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NE</code> : Not equal. <code>NE</code> is supported for all
     * datatypes, including lists and maps.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, Binary, String Set, Number Set, or Binary Set. If an
     * item contains an <i>AttributeValue</i> of a different type than the one
     * provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not equal <code>{"NS":["6", "2", "1"]}</code>
     * .
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LE</code> : Less than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>LT</code> : Less than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String, Number, or Binary (not a set type). If an item contains an
     * <i>AttributeValue</i> element of a different type than the one provided
     * in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GE</code> : Greater than or equal.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>GT</code> : Greater than.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If an item
     * contains an <i>AttributeValue</i> element of a different type than the
     * one provided in the request, the value does not match. For example,
     * <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>. Also,
     * <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>.
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>NOT_NULL</code> : The attribute exists. <code>NOT_NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the existence of an attribute, not its data type.
     * If the data type of attribute "<code>a</code>" is null, and you evaluate
     * it using <code>NOT_NULL</code>, the result is a Boolean <i>true</i>. This
     * result is because the attribute "<code>a</code>" exists; its data type is
     * not relevant to the <code>NOT_NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>NULL</code> : The attribute does not exist. <code>NULL</code> is
     * supported for all datatypes, including lists and maps.
     * </p>
     * <note>
     * <p>
     * This operator tests for the nonexistence of an attribute, not its data
     * type. If the data type of attribute "<code>a</code>" is null, and you
     * evaluate it using <code>NULL</code>, the result is a Boolean
     * <i>false</i>. This is because the attribute "<code>a</code>" exists; its
     * data type is not relevant to the <code>NULL</code> comparison operator.
     * </p>
     * </note></li>
     * <li>
     * <p>
     * <code>CONTAINS</code> : Checks for a subsequence, or value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is of type String, then the operator checks
     * for a substring match. If the target attribute of the comparison is of
     * type Binary, then the operator looks for a subsequence of the target that
     * matches the input. If the target attribute of the comparison is a set ("
     * <code>SS</code>", "<code>NS</code>", or "<code>BS</code>"), then the
     * operator evaluates to true if it finds an exact match with any member of
     * the set.
     * </p>
     * <p>
     * CONTAINS is supported for lists: When evaluating "
     * <code>a CONTAINS b</code>", "<code>a</code>" can be a list; however, "
     * <code>b</code>" cannot be a set, a map, or a list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>NOT_CONTAINS</code> : Checks for absence of a subsequence, or
     * absence of a value in a set.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i>
     * element of type String, Number, or Binary (not a set type). If the target
     * attribute of the comparison is a String, then the operator checks for the
     * absence of a substring match. If the target attribute of the comparison
     * is Binary, then the operator checks for the absence of a subsequence of
     * the target that matches the input. If the target attribute of the
     * comparison is a set ("<code>SS</code>", "<code>NS</code>", or "
     * <code>BS</code>"), then the operator evaluates to true if it <i>does
     * not</i> find an exact match with any member of the set.
     * </p>
     * <p>
     * NOT_CONTAINS is supported for lists: When evaluating "
     * <code>a NOT CONTAINS b</code>", "<code>a</code>
     * " can be a list; however, "<code>b</code>" cannot be a set, a map, or a
     * list.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BEGINS_WITH</code> : Checks for a prefix.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain only one <i>AttributeValue</i> of
     * type String or Binary (not a Number or a set type). The target attribute
     * of the comparison must be of type String or Binary (not a Number or a set
     * type).
     * </p>
     * <p/></li>
     * <li>
     * <p>
     * <code>IN</code> : Checks for matching elements within two sets.
     * </p>
     * <p>
     * <i>AttributeValueList</i> can contain one or more <i>AttributeValue</i>
     * elements of type String, Number, or Binary (not a set type). These
     * attributes are compared against an existing set type attribute of an
     * item. If any elements of the input set are present in the item attribute,
     * the expression evaluates to true.
     * </p>
     * </li>
     * <li>
     * <p>
     * <code>BETWEEN</code> : Greater than or equal to the first value, and less
     * than or equal to the second value.
     * </p>
     * <p>
     * <i>AttributeValueList</i> must contain two <i>AttributeValue</i> elements
     * of the same type, either String, Number, or Binary (not a set type). A
     * target attribute matches if the target value is greater than, or equal
     * to, the first element and less than, or equal to, the second element. If
     * an item contains an <i>AttributeValue</i> element of a different type
     * than the one provided in the request, the value does not match. For
     * example, <code>{"S":"6"}</code> does not compare to
     * <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not compare to
     * <code>{"NS":["6", "2", "1"]}</code>
     * </p>
     * </li>
     * </ul>
     * <p>
     * For usage examples of <i>AttributeValueList</i> and
     * <i>ComparisonOperator</i>, see <a href=
     * "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     * >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB Developer
     * Guide</i>.
     * </p>
     * <p>
     * Returns a reference to this object so that method calls can be chained
     * together.
     * <p>
     * <b>Constraints:</b><br/>
     * <b>Allowed Values: </b>EQ, NE, IN, LE, LT, GE, GT, BETWEEN, NOT_NULL,
     * NULL, CONTAINS, NOT_CONTAINS, BEGINS_WITH
     *
     * @param comparisonOperator <p>
     *            A comparator for evaluating attributes. For example, equals,
     *            greater than, less than, etc.
     *            </p>
     *            <p>
     *            The following comparison operators are available:
     *            </p>
     *            <p>
     *            <code>EQ | NE | LE | LT | GE | GT | NOT_NULL | NULL | CONTAINS | NOT_CONTAINS | BEGINS_WITH | IN | BETWEEN</code>
     *            </p>
     *            <p>
     *            The following are descriptions of each comparison operator.
     *            </p>
     *            <ul>
     *            <li>
     *            <p>
     *            <code>EQ</code> : Equal. <code>EQ</code> is supported for all
     *            datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, Binary,
     *            String Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NE</code> : Not equal. <code>NE</code> is supported for
     *            all datatypes, including lists and maps.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, Binary, String
     *            Set, Number Set, or Binary Set. If an item contains an
     *            <i>AttributeValue</i> of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            equal <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LE</code> : Less than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>LT</code> : Less than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String, Number, or Binary (not a
     *            set type). If an item contains an <i>AttributeValue</i>
     *            element of a different type than the one provided in the
     *            request, the value does not match. For example,
     *            <code>{"S":"6"}</code> does not equal <code>{"N":"6"}</code>.
     *            Also, <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GE</code> : Greater than or equal.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>GT</code> : Greater than.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If an item contains an
     *            <i>AttributeValue</i> element of a different type than the one
     *            provided in the request, the value does not match. For
     *            example, <code>{"S":"6"}</code> does not equal
     *            <code>{"N":"6"}</code>. Also, <code>{"N":"6"}</code> does not
     *            compare to <code>{"NS":["6", "2", "1"]}</code>.
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>NOT_NULL</code> : The attribute exists.
     *            <code>NOT_NULL</code> is supported for all datatypes,
     *            including lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the existence of an attribute, not its
     *            data type. If the data type of attribute "<code>a</code>" is
     *            null, and you evaluate it using <code>NOT_NULL</code>, the
     *            result is a Boolean <i>true</i>. This result is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NOT_NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>NULL</code> : The attribute does not exist.
     *            <code>NULL</code> is supported for all datatypes, including
     *            lists and maps.
     *            </p>
     *            <note>
     *            <p>
     *            This operator tests for the nonexistence of an attribute, not
     *            its data type. If the data type of attribute "<code>a</code>"
     *            is null, and you evaluate it using <code>NULL</code>, the
     *            result is a Boolean <i>false</i>. This is because the
     *            attribute "<code>a</code>" exists; its data type is not
     *            relevant to the <code>NULL</code> comparison operator.
     *            </p>
     *            </note></li>
     *            <li>
     *            <p>
     *            <code>CONTAINS</code> : Checks for a subsequence, or value in
     *            a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is of type String, then the operator checks for a
     *            substring match. If the target attribute of the comparison is
     *            of type Binary, then the operator looks for a subsequence of
     *            the target that matches the input. If the target attribute of
     *            the comparison is a set ("<code>SS</code>", "<code>NS</code>
     *            ", or "<code>BS</code>"), then the operator evaluates to true
     *            if it finds an exact match with any member of the set.
     *            </p>
     *            <p>
     *            CONTAINS is supported for lists: When evaluating "
     *            <code>a CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>NOT_CONTAINS</code> : Checks for absence of a
     *            subsequence, or absence of a value in a set.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> element of type String, Number, or
     *            Binary (not a set type). If the target attribute of the
     *            comparison is a String, then the operator checks for the
     *            absence of a substring match. If the target attribute of the
     *            comparison is Binary, then the operator checks for the absence
     *            of a subsequence of the target that matches the input. If the
     *            target attribute of the comparison is a set ("<code>SS</code>
     *            ", "<code>NS</code>", or "<code>BS</code>"), then the operator
     *            evaluates to true if it <i>does not</i> find an exact match
     *            with any member of the set.
     *            </p>
     *            <p>
     *            NOT_CONTAINS is supported for lists: When evaluating "
     *            <code>a NOT CONTAINS b</code>", "<code>a</code>
     *            " can be a list; however, "<code>b</code>" cannot be a set, a
     *            map, or a list.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BEGINS_WITH</code> : Checks for a prefix.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain only one
     *            <i>AttributeValue</i> of type String or Binary (not a Number
     *            or a set type). The target attribute of the comparison must be
     *            of type String or Binary (not a Number or a set type).
     *            </p>
     *            <p/></li>
     *            <li>
     *            <p>
     *            <code>IN</code> : Checks for matching elements within two
     *            sets.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> can contain one or more
     *            <i>AttributeValue</i> elements of type String, Number, or
     *            Binary (not a set type). These attributes are compared against
     *            an existing set type attribute of an item. If any elements of
     *            the input set are present in the item attribute, the
     *            expression evaluates to true.
     *            </p>
     *            </li>
     *            <li>
     *            <p>
     *            <code>BETWEEN</code> : Greater than or equal to the first
     *            value, and less than or equal to the second value.
     *            </p>
     *            <p>
     *            <i>AttributeValueList</i> must contain two
     *            <i>AttributeValue</i> elements of the same type, either
     *            String, Number, or Binary (not a set type). A target attribute
     *            matches if the target value is greater than, or equal to, the
     *            first element and less than, or equal to, the second element.
     *            If an item contains an <i>AttributeValue</i> element of a
     *            different type than the one provided in the request, the value
     *            does not match. For example, <code>{"S":"6"}</code> does not
     *            compare to <code>{"N":"6"}</code>. Also,
     *            <code>{"N":"6"}</code> does not compare to
     *            <code>{"NS":["6", "2", "1"]}</code>
     *            </p>
     *            </li>
     *            </ul>
     *            <p>
     *            For usage examples of <i>AttributeValueList</i> and
     *            <i>ComparisonOperator</i>, see <a href=
     *            "http://docs.aws.amazon.com/amazondynamodb/latest/developerguide/LegacyConditionalParameters.html"
     *            >Legacy Conditional Parameters</a> in the <i>Amazon DynamoDB
     *            Developer Guide</i>.
     *            </p>
     * @return A reference to this updated object so that method calls can be
     *         chained together.
     * @see ComparisonOperator
     */
    public Condition withComparisonOperator(ComparisonOperator comparisonOperator) {
        this.comparisonOperator = comparisonOperator.toString();
        return this;
    }

    /**
     * Returns a string representation of this object; useful for testing and
     * debugging.
     *
     * @return A string representation of this object.
     * @see java.lang.Object#toString()
     */
    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append("{");
        if (getAttributeValueList() != null)
            sb.append("AttributeValueList: " + getAttributeValueList() + ",");
        if (getComparisonOperator() != null)
            sb.append("ComparisonOperator: " + getComparisonOperator());
        sb.append("}");
        return sb.toString();
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int hashCode = 1;

        hashCode = prime * hashCode
                + ((getAttributeValueList() == null) ? 0 : getAttributeValueList().hashCode());
        hashCode = prime * hashCode
                + ((getComparisonOperator() == null) ? 0 : getComparisonOperator().hashCode());
        return hashCode;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;

        if (obj instanceof Condition == false)
            return false;
        Condition other = (Condition) obj;

        if (other.getAttributeValueList() == null ^ this.getAttributeValueList() == null)
            return false;
        if (other.getAttributeValueList() != null
                && other.getAttributeValueList().equals(this.getAttributeValueList()) == false)
            return false;
        if (other.getComparisonOperator() == null ^ this.getComparisonOperator() == null)
            return false;
        if (other.getComparisonOperator() != null
                && other.getComparisonOperator().equals(this.getComparisonOperator()) == false)
            return false;
        return true;
    }
}