594 words

javax.persistence.OrderBy - JPA annotation

javax.persistence
Annotation OrderBy

Target:
Fields (including property get methods)
Specifies the ordering of the elements of a collection valued association or element collection at the point when the association or collection is retrieved.

The syntax of the value ordering element is an orderby_list, as follows:

    orderby_list::= orderby_item [,orderby_item]*
    orderby_item::= [property_or_field_name] [ASC | DESC]

If ASC or DESC is not specified, ASC (ascending order) is assumed.

If the ordering element is not specified for an entity association, ordering by the primary key of the associated entity is assumed.

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.

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.

The OrderBy annotation may be applied to an element collection. When OrderBy 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.

The OrderBy annotation is not used when an order column is specified.

Example 1:

 
    @Entity 
    public class Course {
       ...
       @ManyToMany
       @OrderBy("lastname ASC")
       public List<Student> getStudents() {...};
       ...
    }

Example 2:

    @Entity 
    public class Student {
       ...
       @ManyToMany(mappedBy="students")
       @OrderBy // ordering by primary key is assumed
       public List<Course> getCourses() {...};
       ...
    }

Example 3:

    @Entity 
    public class Person {
         ...
       @ElementCollection
       @OrderBy("zipcode.zip, zipcode.plusFour")
       public Set<Address> getResidences() {...};
       ...
    }
 
    @Embeddable 
    public class Address {
       protected String street;
       protected String city;
       protected String state;
       @Embedded protected Zipcode zipcode;
    }
 
    @Embeddable 
    public class Zipcode {
       protected String zip;
       protected String plusFour;
    }

Since:
JPA 1.0
See Also:
OrderColumn
String value
An orderby_list.
An orderby_list. Specified as follows:
    orderby_list::= orderby_item [,orderby_item]*
    orderby_item::= [property_or_field_name] [ASC | DESC]

If ASC or DESC is not specified, ASC (ascending order) is assumed.

If the ordering element is not specified, ordering by the primary key of the associated entity is assumed.

Default value:
""
Since:
JPA 1.0

This documentation page is derived (with some adjustments) from the open source JPA 2 RI (EclipseLink)
and is available under the terms of the Eclipse Public License, v. 1.0 and Eclipse Distribution License, v. 1.0.
Object Relational Mapping (ORM) JPA 2 providers include Hibernate, EclipseLink, TopLink, OpenJPA and DataNucleus.
Object DB is not an ORM JPA implementation but an Object Database for Java with built in JPA 2 support.