CollectionIsEmptyMethod.java

/**********************************************************************
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.method;

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

import org.datanucleus.api.ApiAdapter;
import org.datanucleus.exceptions.NucleusException;
import org.datanucleus.exceptions.NucleusUserException;
import org.datanucleus.metadata.AbstractMemberMetaData;
import org.datanucleus.store.rdbms.mapping.java.JavaTypeMapping;
import org.datanucleus.store.rdbms.sql.expression.BooleanLiteral;
import org.datanucleus.store.rdbms.sql.expression.CollectionExpression;
import org.datanucleus.store.rdbms.sql.expression.CollectionLiteral;
import org.datanucleus.store.rdbms.sql.expression.SQLExpression;
import org.datanucleus.util.Localiser;

/**
 * Method for evaluating {collExpr1}.isEmpty().
 * Returns a BooleanExpression, utilising the size() expression. So the SQL will be something like
 * <PRE>
 * (SELECT COUNT(*) FROM COLLTABLE A0_SUB WHERE A0_SUB.OWNER_ID_OID = A0.OWNER_ID) = 0
 * </PRE>
 */
public class CollectionIsEmptyMethod extends AbstractSQLMethod
{
    /* (non-Javadoc)
     * @see org.datanucleus.store.rdbms.sql.method.SQLMethod#getExpression(org.datanucleus.store.rdbms.sql.expression.SQLExpression, java.util.List)
     */
    public SQLExpression getExpression(SQLExpression expr, List<SQLExpression> args)
    {
        if (args != null && args.size() > 0)
        {
            throw new NucleusException(Localiser.msg("060015", "isEmpty", "CollectionExpression"));
        }

        if (expr instanceof CollectionLiteral)
        {
            Collection coll = (Collection)((CollectionLiteral)expr).getValue();
            boolean isEmpty = (coll == null || coll.size() == 0);
            JavaTypeMapping m = exprFactory.getMappingForType(boolean.class, false);
            return new BooleanLiteral(stmt, m, isEmpty ? Boolean.TRUE : Boolean.FALSE);
        }

        AbstractMemberMetaData mmd = ((CollectionExpression)expr).getJavaTypeMapping().getMemberMetaData();
        if (mmd.isSerialized())
        {
            throw new NucleusUserException("Cannot perform Collection.isEmpty when the collection is being serialised");
        }

        ApiAdapter api = stmt.getRDBMSManager().getApiAdapter();
        Class elementType = clr.classForName(mmd.getCollection().getElementType());
        if (!api.isPersistable(elementType) && mmd.getJoinMetaData() == null)
        {
            throw new NucleusUserException("Cannot perform Collection.isEmpty when the collection<Non-Persistable> is not in a join table");
        }

        SQLExpression sizeExpr = exprFactory.invokeMethod(stmt, Collection.class.getName(), "size", expr, args);
        JavaTypeMapping mapping = exprFactory.getMappingForType(Integer.class, true);
        SQLExpression zeroExpr = exprFactory.newLiteral(stmt, mapping, 0);
        return sizeExpr.eq(zeroExpr);
    }
}