ExistsExpression.java

/*******************************************************************************
 * Copyright (c) 2006, 2015 Oracle and/or its affiliates. All rights reserved.
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 and Eclipse Distribution License v. 1.0
 * which accompanies this distribution.
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     Oracle - initial API and implementation
 *
 ******************************************************************************/
package org.eclipse.persistence.jpa.jpql.parser;

import org.eclipse.persistence.jpa.jpql.ExpressionTools;
import org.eclipse.persistence.jpa.jpql.WordParser;

/**
 * An <b>EXISTS</b> expression is a predicate that is <code>true</code> only if the result of the
 * subquery consists of one or more values and that is <code>false</code> otherwise.
 *
 * <div><b>BNF:</b> <code>exists_expression ::= [NOT] EXISTS(subquery)</code><p></div>
 *
 * @version 2.5
 * @since 2.3
 * @author Pascal Filion
 */
public final class ExistsExpression extends AbstractSingleEncapsulatedExpression {

    /**
     * The actual <b>NOT</b> identifier found in the string representation of the JPQL query.
     */
    private String notIdentifier;

    /**
     * Creates a new <code>ExistsExpression</code>.
     *
     * @param parent The parent of this expression
     */
    public ExistsExpression(AbstractExpression parent) {
        super(parent, EXISTS);
    }

    /**
     * {@inheritDoc}
     */
    public void accept(ExpressionVisitor visitor) {
        visitor.visit(this);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public String getEncapsulatedExpressionQueryBNFId() {
        return SubqueryBNF.ID;
    }

    /**
     * Returns the actual <b>NOT</b> identifier found in the string representation of the JPQL query,
     * which has the actual case that was used.
     *
     * @return The <b>NOT</b> identifier that was actually parsed, or an empty string if it was not
     * parsed
     */
    public String getActualNotIdentifier() {
        return (notIdentifier != null) ? notIdentifier : ExpressionTools.EMPTY_STRING;
    }

    /**
     * {@inheritDoc}
     */
    public JPQLQueryBNF getQueryBNF() {
        return getQueryBNF(ExistsExpressionBNF.ID);
    }

    /**
     * Determines whether the identifier <b>NOT</b> was parsed.
     *
     * @return <code>true</code> if the identifier <b>NOT</b> was parsed; <code>false</code> otherwise
     */
    public boolean hasNot() {
        return (notIdentifier != null);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected void parse(WordParser wordParser, boolean tolerant) {

        // Parse 'NOT'
        if (wordParser.startsWithIgnoreCase('N')) {
            int position = wordParser.position();
            notIdentifier = wordParser.substring(position, position + 3);
            setText(NOT_EXISTS);
        }

        super.parse(wordParser, tolerant);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    protected AbstractExpression parse(WordParser wordParser, String queryBNFId, boolean tolerant) {

        if (tolerant) {
            return super.parse(wordParser, queryBNFId, tolerant);
        }

        SimpleSelectStatement expression = new SimpleSelectStatement(this);
        expression.parse(wordParser, tolerant);
        return expression;
    }
}