Jump to: navigation, search

Difference between revisions of "EclipseLink/UserGuide/JPA/Basic JPA Development/Entities/Ids/EmbeddedId"

m
(@EmbeddedId)
Line 20: Line 20:
 
* It is serializable.
 
* It is serializable.
 
* It defines <tt>equals</tt> and <tt>hashCode</tt> methods. The semantics of value equality for these methods must be consistent with the database equality for the database types to which the key is mapped.
 
* It defines <tt>equals</tt> and <tt>hashCode</tt> methods. The semantics of value equality for these methods must be consistent with the database equality for the database types to which the key is mapped.
 +
* An instance of the <code>EmbeddedId</code> is used with the <code>EntityManager find()</code> operation, to find an entity by its id.
 +
  
 
Alternatively, you can make the composite primary key class a nonembedded class (see [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/IdClass|@IdClass]]).
 
Alternatively, you can make the composite primary key class a nonembedded class (see [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/IdClass|@IdClass]]).
Line 71: Line 73:
 
======''Example: @EmbeddedId Annotation''======
 
======''Example: @EmbeddedId Annotation''======
 
<source lang="java">
 
<source lang="java">
@Entity
+
@Entity
public class Employee implements Serializable{
+
public class Employee implements Serializable {
 
   
 
   
    EmployeePK primaryKey;
+
    @EmbeddedId
 +
    EmployeePK primaryKey;
 
   
 
   
    public Employee {
+
    public Employee {
    }
+
    }
 
   
 
   
    @EmbeddedId
+
    public EmployeePK getPrimaryKey() {
    public EmployeePK getPrimaryKey() {
+
        return primaryKey:
        return primaryKey:
+
    }
    }
+
 
   
 
   
    public void setPrimaryKey(EmployeePK pk) {
+
    public void setPrimaryKey(EmployeePK pk) {
        primaryKey = pk;
+
        primaryKey = pk;
    }
+
    }
+
 
    ...
+
    ...
}
+
}
 +
</source>
 +
 
 +
======''Example: <code>embedded-id</code> XML''======
 +
<source lang="xml">
 +
<entity class="Employee">
 +
    <attributes>
 +
        <embedded-id name="primaryKey"/>
 +
    </attributes>
 +
</entity>
 
</source>
 
</source>
  

Revision as of 09:18, 9 June 2011

EclipseLink JPA

link="http://wiki.eclipse.org/EclipseLink"
EclipseLink
Website
Download
Community
Mailing ListForumsIRC
Bugzilla
Open
Help Wanted
Bug Day
Contribute
Browse Source

Elug api package icon.png Key API

@EmbeddedId

Use the @EmbeddedId annotation to specify an embeddable composite primary key class (usually made up of two or more primitive or JDK object types) owned by the entity.

Elug note icon.png

Note: Composite primary keys typically arise during mapping from legacy databases when the database key is comprised of several columns.

A composite primary key class has the following characteristics:

  • It is a POJO class.
  • It is a public class with a public no-argument constructor.
  • If you use property-based access, the properties of the primary key class are public or protected.
  • It is serializable.
  • It defines equals and hashCode methods. The semantics of value equality for these methods must be consistent with the database equality for the database types to which the key is mapped.
  • An instance of the EmbeddedId is used with the EntityManager find() operation, to find an entity by its id.


Alternatively, you can make the composite primary key class a nonembedded class (see @IdClass).

The @EmbeddedId annotation does not have attributes.

This example shows a typical composite primary key class annotated with @Embeddable. The Usage of @EmbeddedId Annotation example shows how to configure an entity with this embeddable composite primary key class using the @EmbeddedId annotation.

Example: Embeddable Composite Primary Key Class
 public class EmployeePK implements Serializable {
 
     private String empName;
     private long empID;
 
     public EmployeePK() {
     }
 
     public String getName() {
         return this.empName;
     }
 
     public void setName(String name) {
         this.empName = name;
     }
 
     public long getId() {
         return this.empID;
     }
 
     public void setId(long id) {
         this.empID = id;
     }
 
     public int hashCode() {
         return (int)this.empName.hashCode()+ this.empID;
     }
 
     public boolean equals(Object obj) {
         if (obj == this) return true;
         if (!(obj instanceof EmployeePK)) return false;
         if (obj == null) return false;
         EmployeePK pk = (EmployeePK) obj;
         return pk.empID == this.empID && pk.empName.equals(this.empName);
     }
 }

Example: @EmbeddedId Annotation
@Entity
public class Employee implements Serializable {
 
    @EmbeddedId
    EmployeePK primaryKey;
 
    public Employee {
    }
 
    public EmployeePK getPrimaryKey() {
        return primaryKey:
    }
 
    public void setPrimaryKey(EmployeePK pk) {
        primaryKey = pk;
    }
 
    ...
}
Example: embedded-id XML
<entity class="Employee">
    <attributes>
        <embedded-id name="primaryKey"/>
    </attributes>
</entity>
Elug javaspec icon.gif

For more information, see 1.1.15 "EmbeddedId Annotation" in the JPA Specification.


Eclipselink-logo.gif
Version: 2.2.0 DRAFT
Other versions...