AbstractSelectClauseStateObject.java

/*******************************************************************************
 * Copyright (c) 2011, 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.tools.model.query;

import org.eclipse.persistence.jpa.jpql.parser.AbstractSelectClause;

/**
 * This state object represents the abstract definition of a <code><b>SELECT</b></code> clause,
 * which is either the <code>SELECT</code> clause of the top-level query or of a subquery.
 *
 * @see AbstractSelectStatementStateObject
 * @see SelectClauseStateObject
 *
 * @see AbstractSelectClause
 *
 * @version 2.4
 * @since 2.4
 * @author Pascal Filion
 */
@SuppressWarnings("nls")
public abstract class AbstractSelectClauseStateObject extends AbstractStateObject {

    /**
     * Determines whether the <code><b>DISTINCT</b></code> keyword is part of the query, which is
     * used to return only distinct (different) values.
     */
    private boolean distinct;

    /**
     * Notifies the distinct property has changed.
     */
    public static final String DISTINCT_PROPERTY = "distinct";

    /**
     * Creates a new <code>AbstractSelectClauseStateObject</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>
     */
    protected AbstractSelectClauseStateObject(AbstractSelectStatementStateObject parent) {
        super(parent);
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public AbstractSelectClause getExpression() {
        return (AbstractSelectClause) super.getExpression();
    }

    /**
     * Returns the {@link AbstractFromClauseStateObject} representing the <b>FROM</b> clause.
     *
     * @return The state object representing the <b>FROM</b> clause
     */
    public AbstractFromClauseStateObject getFromClause() {
        return getParent().getFromClause();
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public AbstractSelectStatementStateObject getParent() {
        return (AbstractSelectStatementStateObject) super.getParent();
    }

    /**
     * Gets whether the <code>DISTINCT</code> keyword is part of the query, which is used to
     * return only distinct (different) values
     */
    public boolean hasDistinct() {
        return distinct;
    }

    /**
     * Determines whether this <code><b>SELECT</b></code> clause has a select item defined (only one
     * can be set for a subquery's <code><b>SELECT</b></code> clause and many for a top-level query).
     *
     * @return <code>true</code> if this state object has children; <code>false</code> otherwise
     */
    public abstract boolean hasSelectItem();

    /**
     * {@inheritDoc}
     */
    @Override
    public boolean isEquivalent(StateObject stateObject) {

        if (super.isEquivalent(stateObject)) {
            AbstractSelectClauseStateObject select = (AbstractSelectClauseStateObject) stateObject;
            return distinct && select.distinct;
        }

        return false;
    }

    /**
     * Parses the given JPQL fragment and create the select item. For the top-level query, the
     * fragment can contain several select items but for a subquery, it can represent only one.
     *
     * @param jpqlFragment The portion of the query representing one or several select items
     */
    public abstract void parse(String jpqlFragment);

    /**
     * Sets whether the <code>DISTINCT</code> keyword should be part of the query, which is used to
     * return only distinct (different) values
     *
     * @param distinct <code>true</code> to add <code>DISTINCT</code> to the query in order to have
     * distinct values; <code>false</code> if it is not required
     */
    public void setDistinct(boolean distinct) {
        boolean oldDistinct = this.distinct;
        this.distinct = distinct;
        firePropertyChanged(DISTINCT_PROPERTY, oldDistinct, distinct);
    }

    /**
     * Changes the state of the <code><b>DISTINCT</b></code> identifier; either adds it if it's not
     * present or removes it if it's present.
     */
    public void toggleDistinct() {
        setDistinct(!hasDistinct());
    }
}