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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:
// 01/19/2010-2.1 Guy Pelletier
// - 211322: Add fetch-group(s) support to the EclipseLink-ORM.XML Schema
// 06/12/2017-2.7 Lukas Jungmann
// - 518155: [jpa22] add support for repeatable annotations
package org.eclipse.persistence.annotations;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.ElementType.TYPE;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import java.lang.annotation.Repeatable;
/**
* A fetch group is a performance enhancement that allows a group of attributes
* of an object to be loaded on demand, which means that the data for an
* attribute might not loaded from the underlying data source until an explicit
* access call for the attribute first occurs. It avoids the wasteful practice
* of loading up all data of the object's attributes, in which the user is
* interested in only partial of them.
*
* A great deal of caution and careful system use case analysis should be use
* when using the fetch group feature, as the extra round-trip would well offset
* the gain from the deferred loading in many cases.
*
* EclipseLink fetch group support is twofold: the pre-defined fetch groups at
* the Entity or MappedSuperclass level; and dynamic (use case) fetch groups at
* the query level.
*
* Fetch groups can only be used when weaving is enabled or when individual
* classes that define them explicitly implement the
* org.eclipse.persistence.queries.FetchGroupTracker interface.
*
* @author Guy Pelletier
* @since EclipseLink 2.1
*/
@Target({TYPE})
@Retention(RUNTIME)
@Repeatable(FetchGroups.class)
public @interface FetchGroup {
/**
* (Required) The fetch group name.
*/
String name();
/**
* (Optional) Indicates whether all relationship attributes
* specified in the fetch group should be loaded.
*/
boolean load() default false;
/**
* (Required) The list of attributes to fetch.
*/
FetchAttribute[] attributes();
}
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