@IdClass and @EmbeddedId

[rani vini]

Can anyone tell what is the difference between @IdClass and @EmbeddedId?

Thanks in advance

[Cameron Wallace McKenzie]

Here's a Compound Primary Key Class using the @Embeddable tag:

package com.examscam.mappings;
import javax.persistence.Embeddable;
/* First Iteration of the CompoundKey Class */
@Embeddable
public class CompoundKey implements 
                             java.io.Serializable{
  private Long userId;
  private Long bankId;
  public CompoundKey() {}
  public CompoundKey(Long user, Long bank) {
    userId = user;
    bankId = bank;
  }

  public Long getBankId() {return bankId;}
  public void setBankId(Long bankId) {
    this.bankId = bankId;
  }
  public Long getUserId() {return userId;}
  public void setUserId(Long userId) {
    this.userId = userId;
  }
}    

(From this Hibernate/JPA Tutorial)

Later, a class can use that compound key:

 
  @Id
  public CompoundKey getId() {return id;}   

ith the @IdClass annotation, you don't declare an instance variable of type CompoundKey, but instead, just define instance variables for each of the primary key fields. You then mark the corresponding getter tags with standard @Id annotations.

 
@Entity
@IdClass(com.examscam.mappings.CompoundKey.class)
public class Fracture {
  Long bankId; 
  Long userId; 
  String bone;
  
  @Id
  public Long getBankId() {return bankId;}
  @Id
  public Long getUserId() {return userId;}
  
  public void setBankId(Long bankId){this.bankId = bankId;}
  public void setUserId(Long userId){this.userId = userId;}
  public String getBone() {return bone;}
  public void setBone(String bone) {this.bone = bone;}
}   

Here's a little bit more detailed explaination about mapping compound primary keys with Hibernate and JPA:

Mapping Composite Keys with the Java Persistence API (JPA)

-Cameron McKenzie