ConstantNode.java

/**
 * Copyright © 2012 Akiban Technologies, Inc.  All rights
 * reserved.
 *
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Public License v1.0 which
 * accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * This program may also be available under different license terms.
 * For more information, see www.akiban.com or contact
 * licensing@akiban.com.
 *
 * Contributors:
 * Akiban Technologies, Inc.
 */

/* The original from which this derives bore the following: */

/*

   Derby - Class org.apache.derby.impl.sql.compile.ConstantNode

   Licensed to the Apache Software Foundation (ASF) under one or more
   contributor license agreements.  See the NOTICE file distributed with
   this work for additional information regarding copyright ownership.
   The ASF licenses this file to you under the Apache License, Version 2.0
   (the "License"); you may not use this file except in compliance with
   the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License 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.akiban.sql.parser;

import com.akiban.sql.StandardException;
import com.akiban.sql.types.TypeId;

/**
 * ConstantNode holds literal constants as well as nulls.
 * <p>
 * A NULL from the parser may not yet know its type; that
 * must be set during binding, as it is for parameters.
 * <p>
 * the DataValueDescriptor methods want to throw exceptions
 * when they are of the wrong type, but to do that they
 * must check typeId when the value is null, rather than
 * the instanceof check they do for returning a valid value.
 * <p>
 * For code generation, we generate a static field.  Then we set the 
 * field be the proper constant expression (something like <code>
 * getDatavalueFactory().getCharDataValue("hello", ...)) </code>)
 * in the constructor of the generated method.  Ideally
 * we would have just 
 */
public abstract class ConstantNode extends ValueNode
{
    Object value;

    /**
     * Initializer for non-numeric types
     *
     * @param typeId The Type ID of the datatype
     * @param nullable True means the constant is nullable
     * @param maximumWidth The maximum number of bytes in the data value
     *
     * @exception StandardException
     */
    public void init(Object typeId,
                     Object nullable,
                     Object maximumWidth) 
            throws StandardException {
        setType((TypeId)typeId,
                ((Boolean)nullable).booleanValue(),
                ((Integer)maximumWidth).intValue());
    }

    /**
     * Fill this node with a deep copy of the given node.
     */
    public void copyFrom(QueryTreeNode node) throws StandardException {
        super.copyFrom(node);

        ConstantNode other = (ConstantNode)node;
        this.value = other.value;       // Assumed to be immutable.
    }

    /**
     * Get the value in this ConstantNode
     */
    public Object getValue() {
        return value;
    }

    /**
     * Set the value in this ConstantNode.
     */
    public void setValue(Object value) {
        this.value = value;
    }

    /**
     * Convert this object to a String.  See comments in QueryTreeNode.java
     * for how this should be done for tree printing.
     *
     * @return This object as a String
     */

    public String toString() {
        return "value: " + value + "\n" +
            super.toString();
    }

    /**
     * Return whether or not this expression tree represents a constant expression.
     *
     * @return Whether or not this expression tree represents a constant expression.
     */
    public boolean isConstantExpression() {
        return true;
    }

    /**
     * Return whether or not this node represents a typed null constant.
     *
     */
    boolean isNull() {
        return (value == null);
    }
                
    protected boolean isEquivalent(ValueNode o) throws StandardException {
        if (isSameNodeType(o)) {
            ConstantNode other = (ConstantNode)o;

            // value can be null which represents a SQL NULL value.
            return ((other.getValue() == null && getValue() == null) || 
                    (other.getValue() != null && other.getValue().equals(getValue())));
        }
        return false;
    }
}