jpa/org.eclipse.persistence.jpa.jpql/src/main/java/org/eclipse/persistence/jpa/jpql/tools/model/query/NullIfExpressionStateObject.java

/*
 * Copyright (c) 2011, 2021 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 v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     Oracle - initial API and implementation
//
package org.eclipse.persistence.jpa.jpql.tools.model.query;

import org.eclipse.persistence.jpa.jpql.parser.NullIfExpression;
import org.eclipse.persistence.jpa.jpql.parser.ScalarExpressionBNF;
import static org.eclipse.persistence.jpa.jpql.parser.Expression.*;

/**
 * <code><b>NULLIF</b></code> returns the first expression if the two expressions are not equal. If
 * the expressions are equal, <code><b>NULLIF</b></code> returns a null value of the type of the
 * first expression.
 * <p>
 * <code><b>NULLIF</b></code> is equivalent to a searched <code><b>CASE</b></code> expression in
 * which the two expressions are equal and the resulting expression is <code><b>NULL</b></code>.
 * <p>
 * Returns the same type as the first expression.
 *
 * <div><p><b>BNF:</b> <code>nullif_expression::= NULLIF(scalar_expression, scalar_expression)</code></p></div>
 *
 * @see NullIfExpression
 *
 * @version 2.4
 * @since 2.4
 * @author Pascal Filion
 */
public class NullIfExpressionStateObject extends AbstractDoubleEncapsulatedExpressionStateObject {

    /**
     * Creates a new <code>NullIfExpressionStateObject</code>.
     *
     * @param parent The parent of this state object, which cannot be <code>null</code>
     * @exception NullPointerException The given parent cannot be <code>null</code>
     */
    public NullIfExpressionStateObject(StateObject parent) {
        super(parent);
    }

    /**
     * Creates a new <code>NullIfExpressionStateObject</code>.
     *
     * @param parent The parent of this state object, which cannot be <code>null</code>
     * @param firstStateObject The {@link StateObject} representing the first expression
     * @param secondStateObject The {@link StateObject} representing the second expression
     * @exception NullPointerException The given parent cannot be <code>null</code>
     */
    public NullIfExpressionStateObject(StateObject parent,
                                       StateObject firstStateObject,
                                       StateObject secondStateObject) {

        super(parent, firstStateObject, secondStateObject);
    }

    /**
     * Creates a new <code>NullIfExpressionStateObject</code>.
     *
     * @param parent The parent of this state object, which cannot be <code>null</code>
     * @param firstJpqlFragment  The string representation of the first encapsulated expression to
     * parse and to convert into a {@link StateObject} representation
     * @param secondJpqlFragment  The string representation of the second encapsulated expression to
     * parse and to convert into a {@link StateObject} representation
     * @exception NullPointerException The given parent cannot be <code>null</code>
     */
    public NullIfExpressionStateObject(StateObject parent,
                                       String firstJpqlFragment,
                                       String secondJpqlFragment) {

        super(parent, firstJpqlFragment, secondJpqlFragment);
    }

    @Override
    public void accept(StateObjectVisitor visitor) {
        visitor.visit(this);
    }

    @Override
    public NullIfExpression getExpression() {
        return (NullIfExpression) super.getExpression();
    }

    @Override
    protected String getFirstQueryBNFId() {
        return ScalarExpressionBNF.ID;
    }

    @Override
    public String getIdentifier() {
        return NULLIF;
    }

    @Override
    protected String getSecondQueryBNFId() {
        return ScalarExpressionBNF.ID;
    }

    /**
     * Keeps a reference of the {@link NullIfExpression parsed object} object, which should only be
     * done when this object is instantiated during the conversion of a parsed JPQL query into
     * {@link StateObject StateObjects}.
     *
     * @param expression The {@link NullIfExpression parsed object} representing a <code><b>NULLIF</b></code>
     * expression
     */
    public void setExpression(NullIfExpression expression) {
        super.setExpression(expression);
    }
}