Modify entity before flush

Question

Is it possible to update some column before every flush to database? I have modifiedOn and modifiedBy columns and want to update them on every DB update, similar to DB trigger. Is it possible with JPA?

Answer 1

Disclaimer: The following works only with Hibernate / JPA.

You can update the modifiedOn property like this with JPA:

public class Entity {

     private Date modifiedOn;

     @PreUpdate 
     @PrePersist
     public void updateModified() {
         modifiedOn = new Date();
     }
}

As for the modifiedBy, it is a little bit trickier since the JPA spec discourages references to other entities in the lifecycle callback methods. Furthermore, you would need some knowledge of the current user, which probably belongs to the service layer.

You could use an EntityListener like this (however, this still uses the callback methods)

@Entity
@EntityListeners({MyListener.class})
public class MyEntity {
    Date modifiedOn;
    User modifiedBy;
    ...
}

An in the EntityListener:

public class MyListener {

    CurrentUserProvider provider; // Implement this and make sure it is set

    @PreUpdate
    @PrePersist
    public void updateModifier(MyEntity entity) {
         entity.setModifiedOn(new Date());
         entity.setModifiedBy(provider.getCurrentUser());
    }
}

Answer 2

Obviously JPA has Entity callbacks defined in the spec such as @PrePersist, @PreUpdate. Simple revision of the spec would give you more details