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

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(@IdClass)
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Alternatively, you can make the composite primary key class an embedded class owned by the entity (see [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/EmbeddedId|@EmbeddedId]]).
 
Alternatively, you can make the composite primary key class an embedded class owned by the entity (see [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/EmbeddedId|@EmbeddedId]]).
  
The <tt>@IdClass</tt> annotation has a required attribute <tt>value</tt> that you set to the class to specify this class as a composite primary key class (see [[#@AttributeOverride|@AttributeOverride]]).
+
The <tt>@IdClass</tt> annotation has a required attribute <tt>value</tt> that you set to the class to specify this class as a composite primary key class.
  
 
The [[#Example 18-3|Nonembedded Composite Primary Key Class]] example, below, shows a nonembedded composite primary key class. In this class, fields <tt>empName</tt> and <tt>birthDay</tt> must correspond in name and type to properties in the entity class. The [[#Example 18-4|@IdClass Annotation]] example, below, shows how to configure an entity with this nonembedded composite primary key class using the <tt>@IdClass</tt> annotation. Because entity class fields <tt>empName</tt> and <tt>birthDay</tt> are used in the primary key, you must also annotate them using the <tt>@Id</tt> annotation (see [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/Id|@Id]]).
 
The [[#Example 18-3|Nonembedded Composite Primary Key Class]] example, below, shows a nonembedded composite primary key class. In this class, fields <tt>empName</tt> and <tt>birthDay</tt> must correspond in name and type to properties in the entity class. The [[#Example 18-4|@IdClass Annotation]] example, below, shows how to configure an entity with this nonembedded composite primary key class using the <tt>@IdClass</tt> annotation. Because entity class fields <tt>empName</tt> and <tt>birthDay</tt> are used in the primary key, you must also annotate them using the <tt>@Id</tt> annotation (see [[EclipseLink/UserGuide/JPA/Basic JPA Development/Mapping/Entity/Id|@Id]]).
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     }
 
     }
 
   
 
   
     public long getDateOfBirth() {
+
     public Date getBirthDay() {
 
         return this.birthDay;
 
         return this.birthDay;
 
     }
 
     }
 
   
 
   
     public void setDateOfBirth(Date date) {
+
     public void setBirthDay(Date date) {
 
         this.birthDay = date;
 
         this.birthDay = date;
 
     }
 
     }
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======''Example: @IdClass Annotation''======
 
======''Example: @IdClass Annotation''======
 
<source lang="java">
 
<source lang="java">
  @IdClass (EmployeePK.class)
+
@IdClass (EmployeePK.class)
@Entity
+
@Entity
public class Employee implements Serializable{
+
public class Employee implements Serializable{
+
 
    @Id String empName;
+
  @Id String empName;
    @Id Date birthDay;
+
  @Id Date birthDay;
    ...
+
  ...
}
+
}
 
</source>
 
</source>
  

Revision as of 11:09, 8 June 2011

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Elug api package icon.png Key API

@IdClass

Use the @IdClass annotation to specify a composite primary key class (usually made up of two or more primitive, JDK object types or Entity types) for an entity or MappedSuperclass.

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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.
  • Its fields or properties must correspond in type and name to the entity primary key fields or properties annotated with @Id.

Alternatively, you can make the composite primary key class an embedded class owned by the entity (see @EmbeddedId).

The @IdClass annotation has a required attribute value that you set to the class to specify this class as a composite primary key class.

The Nonembedded Composite Primary Key Class example, below, shows a nonembedded composite primary key class. In this class, fields empName and birthDay must correspond in name and type to properties in the entity class. The @IdClass Annotation example, below, shows how to configure an entity with this nonembedded composite primary key class using the @IdClass annotation. Because entity class fields empName and birthDay are used in the primary key, you must also annotate them using the @Id annotation (see @Id).

Example: Nonembedded Composite Primary Key Class
 public class EmployeePK implements Serializable {
 
     private String empName;
     private Date birthDay;
 
     public EmployeePK() {
     }
 
     public String getName() {
         return this.empName;
     }
 
     public void setName(String name) {
         this.empName = name;
     }
 
     public Date getBirthDay() {
         return this.birthDay;
     }
 
     public void setBirthDay(Date date) {
         this.birthDay = date;
     }
 
     public int hashCode() {
         return (int)this.empName.hashCode();
     }
 
     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.birthDay = this.birthDay && pk.empName.equals(this.empName);
     }
 }

Example: @IdClass Annotation
@IdClass (EmployeePK.class)
@Entity
public class Employee implements Serializable{
 
   @Id String empName;
   @Id Date birthDay;
   ...
}


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For more information, see Section 11.1.19 "IdClass Annotation" in the JPA Specification.


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