How do I map a composite key in Hibernate?

The EmbeddedId and IdClass annotations are used to denote composite primary keys.

The following are some of the rules that is applied for composite primary keys.

• The primary key class must be public and must have a public no-arg constructor.
• The primary key class must be serializable.
• The primary key class must define equals and hashCode methods.

Using EmbeddedId.

@Embeddable
public class EntityKey implements Serializable {
    protected Integer compositeKey1;
    protected Integer compositeKey2;

    public EntityKey() {}

    public EntityKey(Integer key1, Integer key2) {
        this.compositeKey1 = key1;
        this.compositeKey2 = key2;
    }
    // equals, hashCode
}

@Entity
public class HibernateEntity implements Serializable {
    @EmbeddedId
    private EntityKey primaryKey;

    private String description;
    
    //...
}

Using IdClass.

  public class EntityKey implements Serializable {
  protected Integer compositeKey1;
  protected Integer compositeKey2;

  public EntityKey() {}

  public EntityKey(Integer key1, Integer key2) {
      this.compositeKey1 = key1;
      this.compositeKey2 = key2;
  }
  // equals, hashCode
}

@Entity
@IdClass(EntityKey.class)
public class HibernateEntity implements Serializable {
	@Id
	private Integer compositeKey1;
	@Id
	private Integer compositeKey2;

  private String description;
  
  //...
}

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