how to find which attributes have changed before using merge() in EclipseLink?

[nicolas diogo]

hi,

i would like to find out if there is a way of knowing which attribute has changed in an entity managed by EclipseLink.

i have to implement a business rule if different attributes are updated - but i do not know how to 'compare' the new values that were updated against those that exist in the database.

i would appreciate if you could post links to documentation about this. i have searched but i doubt that i am using the correct terminology on this subject.

thanks a lot,

Nicolas

[Hebert Coelho]

There is no way to know that in an automatic way.

If you really need to know the changes you could do a find, and compare each attribute.

[nicolas diogo]

thanks

how do i implement your suggestion of 'find'
i do not really understand what you have meant by it.

[Hebert Coelho]

I would be something like:

public void findChanges(Car car){
    Car savedCar = entityManager.find(Car.class, car.getId());
    if (car.getName().equals(savedCar)) {
        System.out.println("no change were found");
    }

}

[James Sutherland]

After you merge, you can get the objects changeSet (by casting to ChangeTracker if weaving change tracking, or calling UnitOfWork.getCurrentChanges()).

Before the merge, not sure they is a public API, but there is ObjectBuilder.compareForChange (or merge into a temporary persistence context).