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/*
 * Copyright (c) 2011, 2018 Oracle and/or its affiliates. All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v. 2.0 which is available at
 * http://www.eclipse.org/legal/epl-2.0,
 * or the Eclipse Distribution License v. 1.0 which is available at
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * SPDX-License-Identifier: EPL-2.0 OR BSD-3-Clause
 */

// Contributors:
//     James Sutherland - initial API and implementation
package org.eclipse.persistence.annotations;

import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import javax.persistence.Column;

import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * HashPartitioning partitions access to a database cluster by the hash of a field value from the object,
 * such as the object's location, or tenant.
 * The hash indexes into the list of connection pools.
 * All write or read request for object's with that hash value are sent to the server.
 * If a query does not include the field as a parameter, then it can either be sent
 * to all server's and unioned, or left to the sesion's default behavior.
 * 
 * Partitioning can be enabled on an Entity, relationship, query, or session/persistence unit.
 * Partition policies are globally named to allow reuse,
 * the partitioning policy must also be set using the @Partitioned annotation to be used.
 *
 * @see Partitioned
 * @see org.eclipse.persistence.descriptors.partitioning.HashPartitioningPolicy
 * @author James Sutherland
 * @since EclipseLink 2.2
 */
@Target({TYPE, METHOD, FIELD})
@Retention(RUNTIME)
public @interface HashPartitioning {
    /**
     * The name of the partition policy, names must be unique for the persistence unit.
     */
    String name();

    /**
     * The database column or query parameter to partition queries by.
     * This is the table column name, not the class attribute name.
     * The column value must be included in the query and should normally be part of the object's Id.
     * This can also be the name of a query parameter.
     * If a query does not contain the field the query will not be partitioned.
     */
    Column partitionColumn();

    /**
     * List of connection pool names to partition across.
     * Defaults to all defined pools in the ServerSession.
     */
    String[] connectionPools() default {};

    /**
     * Defines if queries that do not contain the partition field should be sent
     * to every database and have the result unioned.
     */
    boolean unionUnpartitionableQueries() default false;
}