PathExpression.java

/*
 * 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 org.apache.openjpa.persistence.query;

/**
 * Interface for operations over objects reached via paths
 */
public interface PathExpression extends Expression {
    /**
     * Return a path expression corresponding to the referenced attribute. It is
     * not permitted to invoke this method on a path expression that corresponds
     * to a multi-valued association or element collection. The path expression
     * on which this method is invoked must correspond to a class containing the
     * referenced attribute.
     *
     * @param attributeName -
     *                      name of the referenced attribute
     * @return path expression
     */
    PathExpression get(String attributeName);

    /**
     * Return an expression that corresponds to the type of the entity. This
     * method can only be invoked on a path expression corresponding to an
     * entity. It is not permitted to invoke this method on a path expression
     * that corresponds to a multi-valued association.
     *
     * @return expression denoting the entity's type
     */
    Expression type();

    /**
     * Return an expression that corresponds to the number of elements
     * association or element collection corresponding to the path expression.
     * This method can only be invoked on a path expression that corresponds to
     * a multi-valued association or to an element collection.
     *
     * @return expression denoting the size
     */
    Expression size();

    /**
     * Add a restriction that the path expression must correspond to an
     * association or element collection that is empty (has no elements). This
     * method can only be invoked on a path expression that corresponds to a
     * multi-valued association or to an element collection.
     *
     * @return predicate corresponding to the restriction
     */
    Predicate isEmpty();

    /**
     * Specify that the avg operation is to be applied. The path expression must
     * correspond to an attribute of a numeric type. It is not permitted to
     * invoke this method on a path expression that corresponds to a
     * multi-valued association or element collection.
     *
     * @return the resulting aggregate
     */
    Aggregate avg();

    /**
     * Specify that the max operation is to be applied. The path expression must
     * correspond to an attribute of an orderable type. It is not permitted to
     * invoke this method on a path expression that corresponds to a
     * multi-valued association or element collection.
     *
     * @return the resulting aggregate
     */
    Aggregate max();

    /**
     * Specify that the min operation is to be applied. The path expression must
     * correspond to an attribute of an orderable type. It is not permitted to
     * invoke this method on a path expression that corresponds to a
     * multi-valued association or element collection.
     *
     * @return the resulting aggregate
     */
    Aggregate min();

    /**
     * Specify that the count operation is to be applied. It is not permitted to
     * invoke this method on a path expression that corresponds to a
     * multi-valued association or element collection.
     *
     * @return the resulting aggregate
     */
    Aggregate count();

    /**
     * Specify that the sum operation is to be applied. The path expression must
     * correspond to an attribute of a numeric type. It is not permitted to
     * invoke this method on a path expression that corresponds to a
     * multi-valued association or element collection.
	 *
	 * @return the resulting aggregate
	 */
	Aggregate sum();
}