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The Java Persistence API (JPA) : a standard interface-based Java model abstraction of persistence, developed by the JCP.

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/*
 * Copyright (c) 2008, 2009, 2011 Oracle, Inc. 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.
 */
package javax.persistence;

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

import static java.lang.annotation.RetentionPolicy.RUNTIME;

/**
 * Used to map the SELECT clause of a SQL query to an entity result. If this annotation is used, the SQL
 * statement should select all of the columns that are mapped to the entity object. This should include
 * foreign key columns to related entities. The results obtained when insufficient data is available are
 * undefined.
 *
 *  *   Example:
 * 
 *   Query q = em.createNativeQuery(
 *       "SELECT o.id, o.quantity, o.item, i.id, i.name, i.description "+
 *           "FROM Order o, Item i " +
 *           "WHERE (o.quantity > 25) AND (o.item = i.id)",
 *       "OrderItemResults");
 *   @SqlResultSetMapping(name="OrderItemResults",
 *       entities={
 *           @EntityResult(entityClass=com.acme.Order.class),
 *           @EntityResult(entityClass=com.acme.Item.class)
 *   })
 * 
 * @see SqlResultSetMapping
 * @since Java Persistence 1.0
 */
@Target({})
@Retention(RUNTIME)
public @interface EntityResult
{

    /** 
     * The class of the result. 
     * @return entity class
     */
    Class entityClass();

    /**
     * Maps the columns specified in the SELECT list of the query to the properties or fields of the entity
     * class.
     * @return fields
     */
    FieldResult[] fields() default {};

    /**
     * Specifies the column name (or alias) of the column in the SELECT list that is used to determine the
     * type of the entity instance.
     * @return disc col
     */
    String discriminatorColumn() default "";
}