Inheritance Mapping

Basically there are 3 types of inheritance mapping. We may use those methods suitably.

• SINGLE_TABLE (default)
• JOINED
• TABLE_PER_CLASS

Model

Compound Primary Keys in HIBERNATE

Most of the time we need only 1 primary key. But there are some situations we may need compound primary keys.
Here in hibernate it is simple. We can use 2 classes into 1 table strategy.

Account.java

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Account {

 private AccountCompoundKey compoundKey;
 private int accBalance;
 
 @Id
 public AccountCompoundKey getCompoundKey() {
  return compoundKey;
 }
 public void setCompoundKey(AccountCompoundKey compoundKey) {
  this.compoundKey = compoundKey;
 }
 public int getAccBalance() {
  return accBalance;
 }
 public void setAccBalance(int accBalance) {
  this.accBalance = accBalance;
 } 
}

One table for 2 or More Classes

In some situations we may need create 1 table out of 2 or more classes. for instance when we map inheritance.

New Annotations :

• @Embeddable : when a class is going to be embedded inside another persistence class we have to annotate the class as embeddable
• @Embedded : When some (object) field is going to persist inside a class. The object type must annotated as embeddable