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JPA-like syntax for annotating POJO classes for persistence via Cassandra's Java driver - API
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/*
 * Copyright (C) 2015-2015 The Helenus Driver Project 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 com.github.helenusdriver.persistence;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

import java.util.Set;

import com.github.helenusdriver.annotation.Keyable;

/**
 * The ClusteringKey annotation indicates the column is a clustering
 * key. The clustering key column determines an index that keeps data in an order
 * for a given partition key.
 * 
 * It is also possible to specify compound clustering keys by annotating multiple
 * fields or properties with the ClusteringKey annotation.
 * 

 * Special support is given to a clustering key defined as {@link Set}. Using
 * such a multi-clustering key enables querying for any of its elements to
 * retrieve the object from the database. Underneath the table, in addition to
 * saving the key as a set in the defined column, the driver will also create
 * another column of the element type as the actual clustering key and create
 * multiple entries in the table; one per element of the multi-key.
 *
 * @copyright 2015-2015 The Helenus Driver Project Authors
 *
 * @author  The Helenus Driver Project Authors
 * @version 1 - Jan 15, 2015 - paouelle - Creation
 *
 * @since 1.0
 */
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Repeatable(ClusteringKeys.class)
@Keyable("table")
@Documented
public @interface ClusteringKey {
  /**
   * The name of the table as defined in {@link Table#name} this clustering key
   * is associated with.
   * 
   * By default, if none specified, the column will be considered a clustering
   * key for all tables defined by the entity unless otherwise overridden.
   *
   * @author paouelle
   *
   * @return the name of table this clustering key is associated with
   */
  String table() default Table.ALL;

  /**
   * Optional order for the clustering key (defaults to ascending).
   *
   * @author paouelle
   *
   * @return the optional order for the clustering key
   */
  Ordering order() default Ordering.ASCENDING;
}