JPA - Tips

###  Orphan Removal and  CascadeType

JPA 2 supports an additional and more aggressive remove cascading mode which can be specified using the orphanRemoval element of the @OneToOne and @OneToMany annotations:

@Entity  
class User{ 
  @OneToOne(orphanRemoval=true) 
  private PhoneNum phoneNum;  
}

The difference between the two settings is in the response to disconnecting a relationship. For example, such as when setting the address field to null or to another Address object.

• If orphanRemoval=true is specified the disconnected Address instance is automatically removed. This is useful for cleaning up dependent objects (e.g.PhoneNum) that should not exist without a
  reference from an owner object (e.g. User).

• If only cascade=CascadeType.REMOVE is specified no automatic action is taken since disconnecting a relationship is not a remove
  operation.

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