/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2009 by Red Hat Inc and/or its affiliates or by
 * third-party contributors as indicated by either @author tags or express
 * copyright attribution statements applied by the authors.  All
 * third-party contributions are distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.ejb.criteria.predicate;
import java.io.Serializable;
import javax.persistence.criteria.Expression;
import org.hibernate.ejb.criteria.CriteriaBuilderImpl;
import org.hibernate.ejb.criteria.CriteriaQueryCompiler;
import org.hibernate.ejb.criteria.ParameterRegistry;
import org.hibernate.ejb.criteria.Renderable;
import org.hibernate.ejb.criteria.expression.UnaryOperatorExpression;

/**
 * Defines a {@link javax.persistence.criteria.Predicate} for checking the
 * nullness state of an expression, aka an <tt>IS [NOT] NULL</tt> predicate.
 * <p/>
 * The <tt>NOT NULL</tt> form can be built by calling the constructor and then
 * calling {@link #not}.
 *
 * @author Steve Ebersole
 */
public class NullnessPredicate
		extends AbstractSimplePredicate
		implements UnaryOperatorExpression<Boolean>, Serializable {
	private final Expression<?> operand;

	/**
	 * Constructs the affirmitive form of nullness checking (<i>IS NULL</i>).  To
	 * construct the negative form (<i>IS NOT NULL</i>) call {@link #not} on the
	 * constructed instance.
	 *
	 * @param criteriaBuilder The query builder from whcih this originates.
	 * @param operand The expression to check.
	 */
	public NullnessPredicate(CriteriaBuilderImpl criteriaBuilder, Expression<?> operand) {
		super( criteriaBuilder );
		this.operand = operand;
	}

	public Expression<?> getOperand() {
		return operand;
	}

	public void registerParameters(ParameterRegistry registry) {
		Helper.possibleParameter( getOperand(), registry );
	}

	public String render(CriteriaQueryCompiler.RenderingContext renderingContext) {
		return ( (Renderable) operand ).render( renderingContext ) + check();
	}

	private String check() {
		return isNegated()
				? " is not null"
				: " is null";
	}

	public String renderProjection(CriteriaQueryCompiler.RenderingContext renderingContext) {
		return render( renderingContext );
	}
}