EmptyCollectionIfNull.java

/*
 * Copyright (C) 2012-2016 DuyHai DOAN
 *
 * 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 info.archinnov.achilles.annotations;

import java.lang.annotation.*;

/**

 * In Cassandra there is no difference between an empty collection/map
 * and a null value for collection/map
 * <br/>
 * <br/>
 * In Java we do make the difference. This annotations allows mapping null values from
 * <strong>Cassandra</strong> into empty collection & map.
 * <br/>
 * <br/>
 * Empty list will default to <strong>ArrayList</strong>.<br/>
 * Empty set will default to <strong>HashSet</strong>.<br/>
 * Empty map will default to <strong>HashMap</strong>.<br/>

 * <pre class="code"><code class="java">
 * {@literal @}Column
 * <strong>{@literal @}EmptyCollectionIfNull</strong>
 * private List<String> friends
 * </code></pre>
 * <br/>

 * This annotation can be used for <strong>nested</strong> collections too:
 * <br/>
 * <pre class="code"><code class="java">
 * {@literal @}Column
 * private Tuple2<Integer,<strong>{@literal @}EmptyCollectionIfNull</strong> List<String>> friends
 * </code></pre>

 * </p>
 *
 * @see <a href="https://github.com/doanduyhai/Achilles/wiki/Achilles-Annotations#emptycollectionifnull" target="_blank">@EmptyCollectionIfNull</a>
 */
@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.FIELD, ElementType.TYPE_USE})
@Documented
public @interface EmptyCollectionIfNull {

}