/*
 * 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
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 * 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
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 */
package org.hibernate.jpa.criteria.predicate;

import java.io.Serializable;
import javax.persistence.criteria.Expression;

import org.hibernate.jpa.criteria.CriteriaBuilderImpl;
import org.hibernate.jpa.criteria.ParameterRegistry;
import org.hibernate.jpa.criteria.Renderable;
import org.hibernate.jpa.criteria.compile.RenderingContext;
import org.hibernate.jpa.criteria.expression.UnaryOperatorExpression;

Defines a Predicate for checking the nullness state of an expression, aka an IS [NOT] NULL predicate.

The NOT NULL form can be built by calling the constructor and then calling AbstractPredicateImpl.not. 
Author:
Steve Ebersole/**
 * 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 (IS NULL).  To
construct the negative form (IS NOT NULL) call AbstractPredicateImpl.not on the constructed instance. 
Params:
criteriaBuilder – The query builder from whcih this originates.
operand – The expression to check./**
	 * 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;
	}

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

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

	@Override
	public String render(boolean isNegated, RenderingContext renderingContext) {
		return ( (Renderable) operand ).render( renderingContext ) + check( isNegated );
	}

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