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Plugin for DataNucleus providing persistence to RDBMS datastores.
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/**********************************************************************
Copyright (c) 2008 Andy Jefferson and others. 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.
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.

Contributors:
    ...
**********************************************************************/
package org.datanucleus.store.rdbms.sql.expression;

import java.util.Collection;
import java.util.List;

import org.datanucleus.store.rdbms.mapping.java.JavaTypeMapping;
import org.datanucleus.store.rdbms.sql.SQLStatement;
import org.datanucleus.store.rdbms.sql.SQLTable;

/**
 * An expression that represents some collection field in a query candidate class, 
 * or a collection field in an object linked from the candidate class by navigation.
 * 
 * When navigated through using contains(expr), the elements of the collection
 * are relationally joined onto the query statement.
 * 
 * 
 * As this is a Collection Expression it works equally for Sets and Lists, and we use CollectionStore 
 * as the backing store interface, so that ListStore and SetStore are equally applicable.
 * 
 */
public class CollectionExpression extends SQLExpression
{
    /**
     * Constructor for an SQL expression for a (field) mapping in a specified table.
     * @param stmt The statement
     * @param table The table in the statement
     * @param mapping The mapping for the field
     */
    public CollectionExpression(SQLStatement stmt, SQLTable table, JavaTypeMapping mapping)
    {
        super(stmt, table, mapping);
    }

    public SQLExpression invoke(String methodName, List args)
    {
        return stmt.getRDBMSManager().getSQLExpressionFactory().invokeMethod(stmt, Collection.class.getName(), 
            methodName, this, args);
    }

    /**
     * Method to return the expression for comparing a collection with a value.
     * Only supports comparisons with null currently.
     * @param expr The value to compare with.
     * @return The expression of equality
     */
    public BooleanExpression eq(SQLExpression expr)
    {
        if (expr instanceof NullLiteral)
        {
            return (BooleanExpression)invoke("isEmpty", null);
        }
        return super.eq(expr);
    }

    /**
     * Method to return the expression for comparing a collection with a value.
     * Only supports comparisons with null currently.
     * @param expr The value to compare with.
     * @return The expression of inequality
     */
    public BooleanExpression ne(SQLExpression expr)
    {
        if (expr instanceof NullLiteral)
        {
            return invoke("isEmpty", null).not();
        }
        return super.ne(expr);
    }
}