src/javax/persistence/OrderBy.java

/*
 * Copyright (c) 2008, 2019 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:
//     Linda DeMichiel - 2.1
//     Linda DeMichiel - 2.0

package javax.persistence;

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

/**
 * Specifies the ordering of the elements of a collection valued
 * association or element collection at the point when the association
 * or collection is retrieved.
 * 
 * <p> The syntax of the <code>value</code> ordering element is an 
 * <code>orderby_list</code>, as follows:
 * 
 * <pre>
 *    orderby_list::= orderby_item [,orderby_item]*
 *    orderby_item::= [property_or_field_name] [ASC | DESC]
 * </pre>
 * 
 * <p> If <code>ASC</code> or <code>DESC</code> is not specified, 
 * <code>ASC</code> (ascending order) is assumed.
 *
 * <p> If the ordering element is not specified for an entity association,
 * ordering by the primary key of the associated entity is assumed.
 *
 * <p> The property or field name must correspond to that of a 
 * persistent property or field of the associated class or embedded class
 * within it.  The properties or fields used in the ordering must correspond to 
 * columns for which comparison operators are supported.
 *
 * <p> The dot (".") notation is used to refer to an attribute within an
 * embedded attribute.  The value of each identifier used with the dot
 * notation is the name of the respective embedded field or property.
 *
 * <p> The <code>OrderBy</code> annotation may be applied to an element
 * collection. When <code>OrderBy</code> is applied to an element collection of
 * basic type, the ordering will be by value of the basic objects and
 * the property or field name is not used. When specifying an ordering
 * over an element collection of embeddable type, the dot notation
 * must be used to specify the attribute or attributes that determine
 * the ordering.  
 *
 * <p> The <code>OrderBy</code> annotation is not used when an order
 * column is specified.
 *
 * 
 * <pre>
 *    Example 1:
 *    
 *    &#064;Entity 
 *    public class Course {
 *       ...
 *       &#064;ManyToMany
 *       &#064;OrderBy("lastname ASC")
 *       public List&#060;Student&#062; getStudents() {...};
 *       ...
 *    }
 *    
 *    Example 2:
 *
 *    &#064;Entity 
 *    public class Student {
 *       ...
 *       &#064;ManyToMany(mappedBy="students")
 *       &#064;OrderBy // ordering by primary key is assumed
 *       public List&#060;Course&#062; getCourses() {...};
 *       ...
 *    }
 *
 *    Example 3: 
 *
 *    &#064;Entity 
 *    public class Person {
 *         ...
 *       &#064;ElementCollection
 *       &#064;OrderBy("zipcode.zip, zipcode.plusFour")
 *       public Set&#060;Address&#062; getResidences() {...};
 *       ...
 *    }
 *  
 *    &#064;Embeddable 
 *    public class Address {
 *       protected String street;
 *       protected String city;
 *       protected String state;
 *       &#064;Embedded protected Zipcode zipcode;
 *    }
 *
 *    &#064;Embeddable 
 *    public class Zipcode {
 *       protected String zip;
 *       protected String plusFour;
 *    }
 * </pre>
 *
 * @see OrderColumn
 *
 * @since 1.0
 */
@Target({METHOD, FIELD}) 
@Retention(RUNTIME)

public @interface OrderBy {

   /**
    * An <code>orderby_list</code>.  Specified as follows:
    *
    * <pre>
    *    orderby_list::= orderby_item [,orderby_item]*
    *    orderby_item::= [property_or_field_name] [ASC | DESC]
    * </pre>
    *
    * <p> If <code>ASC</code> or <code>DESC</code> is not specified,
    * <code>ASC</code> (ascending order) is assumed.
    *
    * <p> If the ordering element is not specified, ordering by
    * the primary key of the associated entity is assumed.
    */
    String value() default "";
}