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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.method;

import java.util.List;

import org.datanucleus.exceptions.NucleusException;
import org.datanucleus.query.expression.Expression;
import org.datanucleus.store.rdbms.sql.SQLStatement;
import org.datanucleus.store.rdbms.sql.expression.BooleanExpression;
import org.datanucleus.store.rdbms.sql.expression.CharacterExpression;
import org.datanucleus.store.rdbms.sql.expression.ExpressionUtils;
import org.datanucleus.store.rdbms.sql.expression.ParameterLiteral;
import org.datanucleus.store.rdbms.sql.expression.SQLExpression;
import org.datanucleus.store.rdbms.sql.expression.SQLLiteral;
import org.datanucleus.store.rdbms.sql.expression.StringExpression;
import org.datanucleus.store.rdbms.sql.expression.StringLiteral;
import org.datanucleus.util.Localiser;

/**
 * Method for evaluating {strExpr1}.startsWith(strExpr2[, numExpr]).
 * Returns a StringExpression that equates to {strExpr1} LIKE {strExpr2}% ESCAPE ...
 */
public class StringStartsWithMethod implements SQLMethod
{
    /* (non-Javadoc)
     * @see org.datanucleus.store.rdbms.sql.method.SQLMethod#getExpression(org.datanucleus.store.rdbms.sql.expression.SQLExpression, java.util.List)
     */
    public SQLExpression getExpression(SQLStatement stmt, SQLExpression expr, List args)
    {
        if (args == null || args.size() == 0 || args.size() > 2)
        {
            throw new NucleusException(Localiser.msg("060003", "startsWith", "StringExpression", 0, "StringExpression/CharacterExpression/Parameter"));
        }

        SQLExpression substrExpr = args.get(0);
        if (!(substrExpr instanceof StringExpression) && !(substrExpr instanceof CharacterExpression) && !(substrExpr instanceof ParameterLiteral))
        {
            throw new NucleusException(Localiser.msg("060003", "startsWith", "StringExpression", 0, "StringExpression/CharacterExpression/Parameter"));
        }
        if (args.size() > 1)
        {
            // SQLExpression numExpr = (SQLExpression)args.get(1);
            // TODO Use numExpr in a SUBSTRING
            if (substrExpr.isParameter())
            {
                // Any pattern expression cannot be a parameter here
                SQLLiteral substrLit = (SQLLiteral)substrExpr;
                stmt.getQueryGenerator().useParameterExpressionAsLiteral(substrLit);
                if (substrLit.getValue() == null)
                {
                    return new BooleanExpression(expr, Expression.OP_LIKE, ExpressionUtils.getEscapedPatternExpression(substrExpr));
                }
            }
            SQLExpression likeSubstrExpr = new StringLiteral(stmt, expr.getJavaTypeMapping(), '%', null);
            return new BooleanExpression(expr, Expression.OP_LIKE, ExpressionUtils.getEscapedPatternExpression(substrExpr).add(likeSubstrExpr));
        }

        // Create a new StringExpression and manually update its SQL
        if (substrExpr.isParameter())
        {
            // Any pattern expression cannot be a parameter here
            SQLLiteral substrLit = (SQLLiteral)substrExpr;
            stmt.getQueryGenerator().useParameterExpressionAsLiteral(substrLit);
            if (substrLit.getValue() == null)
            {
                return new BooleanExpression(expr, Expression.OP_LIKE, ExpressionUtils.getEscapedPatternExpression(substrExpr));
            }
        }
        SQLExpression likeSubstrExpr = new StringLiteral(stmt, expr.getJavaTypeMapping(), '%', null);
        return new BooleanExpression(expr, Expression.OP_LIKE, ExpressionUtils.getEscapedPatternExpression(substrExpr).add(likeSubstrExpr));
    }
}