org.eclipse.persistence.annotations.FetchGroup Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of eclipselink Show documentation

EclipseLink build based upon Git transaction 346465e

There is a newer version: 5.0.0-B05

/*******************************************************************************
 * Copyright (c) 2011, 2013 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 v1.0 and Eclipse Distribution License v. 1.0 
 * which accompanies this distribution. 
 * The Eclipse Public License is available at http://www.eclipse.org/legal/epl-v10.html
 * and the Eclipse Distribution License is available at 
 * http://www.eclipse.org/org/documents/edl-v10.php.
 *
 * Contributors:
 *     01/19/2010-2.1 Guy Pelletier 
 *       - 211322: Add fetch-group(s) support to the EclipseLink-ORM.XML Schema
 ******************************************************************************/  
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;

/**
 * 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)
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();
}