Specifications.java

/*
 * Copyright 2008-2010 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.synyx.hades.domain;

import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Predicate;
import javax.persistence.criteria.Root;


/**
 * Helper class to easily combine {@link Specification} instances.
 * 
 * @author Oliver Gierke
 */
public class Specifications<T> implements Specification<T> {

    private final Specification<T> spec;


    /**
     * Creates a new {@link Specifications} wrapper for the given
     * {@link Specification}.
     * 
     * @param spec
     */
    private Specifications(Specification<T> spec) {

        this.spec = spec;
    }


    /**
     * Simple static factory method to add some syntactic sugar around a
     * {@link Specification}.
     * 
     * @param <T>
     * @param spec
     * @return
     */
    public static <T> Specifications<T> where(Specification<T> spec) {

        return new Specifications<T>(spec);
    }


    /**
     * ANDs the given {@link Specification} to the current one.
     * 
     * @param other
     * @return
     */
    public Specifications<T> and(final Specification<T> other) {

        return new Specifications<T>(new Specification<T>() {

            public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
                    CriteriaBuilder builder) {

                return builder.and(spec.toPredicate(root, query, builder),
                        other.toPredicate(root, query, builder));
            }
        });
    }


    /**
     * ORs the given specification to the current one.
     * 
     * @param other
     * @return
     */
    public Specifications<T> or(final Specification<T> other) {

        return new Specifications<T>(new Specification<T>() {

            public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
                    CriteriaBuilder builder) {

                return builder.or(spec.toPredicate(root, query, builder),
                        other.toPredicate(root, query, builder));
            }
        });
    }


    /**
     * Negates the given {@link Specification}.
     * 
     * @param <T>
     * @param spec
     * @return
     */
    public static <T> Specifications<T> not(final Specification<T> spec) {

        return new Specifications<T>(spec) {

            @Override
            public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
                    CriteriaBuilder builder) {

                return builder.not(spec.toPredicate(root, query, builder));
            }
        };
    }


    /*
     * (non-Javadoc)
     * 
     * @see
     * org.synyx.hades.domain.Specification#toPredicate(javax.persistence.criteria
     * .Root, javax.persistence.criteria.CriteriaQuery,
     * javax.persistence.criteria.CriteriaBuilder)
     */
    public Predicate toPredicate(Root<T> root, CriteriaQuery<?> query,
            CriteriaBuilder builder) {

        return spec.toPredicate(root, query, builder);
    }
}