Question

In my customer entity I would like to save a changedByUserId field. I only want to set this field if one of the other fields of customer has really changed. If I allways set it I force EntityManager to update the customer table because I set the changedByUserId field.

@Entity
@Table....
public class Customer {
    @Id
    private Long cusID;
    @Column
    private String cusNAME;
    @Column
    private Date changed;
    @Column
    private Long changedByUserId;

    @PreUpdate
    private preUpdate() {
        changed = new Date();
        // cannot set changedbyUserId here because no entitymanager 
        // available where i can query the id
    }
}

Does anybody know how to tell EntityManager not to check for changes in the changedByUserID field?

Answer 1

You could make a temporary, transient field, which you’d always set to user id, no matter if the entity gets changed or not:

@Transient
private Long tempUserId;
@Column
private Long changedByUserId;

@PreUpdate
private preUpdate() {
    changed = new Date();
    changedByUserId = tempUserId;
}

This was entity manager will execute @PreUpdate only when one of persistent fields really changed.