Get previous instance in update action

[ovistanciu]

How can I obtain the previous entity values in the EntityHome.update method?

Let's say I have a User entity, with the corresponding UserHome component. When I call the update() method in UserHome, how can I have the initial (unedited) values of the User entity (i.e. those first loaded on the page)?
I need to do some work that needs the old values.

Thank you.

[damianharvey.damianharvey.gmail.com]

I do this by creating a Clone of the entity when it is loaded into the Bean and then comparing the Clone to the instance when I do an update.

I had to write the Clone and Compare methods in full (ie. field by field) as I couldn't find an easy method of creating a non-linked clone (so the Clone won't update when the instance updates)

Cheers,

Damian.

[ovistanciu]

Can I bother you in posting some code or more detailed info? :)

Thank you

[brachie]

Hi,

you could do this by defining a second entityManager and use this one to load the entity from the Database.

Alexander

[damianharvey.damianharvey.gmail.com]

I would post my code but I think Alexander's method has just made mine redundant. I'd try that if I were you. In fact I think I'll be trying it myself.

It would go something like this:

In components.xml

   <persistence:managed-persistence-context name="entityManager" auto-create="true" persistence-unit-jndi-name="java:/MyEntityManagerFactory"/>
   <persistence:managed-persistence-context name="secondaryEntityManager" auto-create="true" persistence-unit-jndi-name="java:/MyEntityManagerFactory"/>

Set your flush mode to manual. And then in your UserHome update() method:

User cloneUser = secondaryEntityManager.find(User.class, getId());
//now do a compare - this you will have to write manually
String differences = UserCompare.compare(getInstance(), cloneUser);

Cheers,

Damian.

[ovistanciu]

Thank you guys. Got it working.

Beer's on me :)

[mars1412]

just a (newbie) question on this (hope it's just my paranoia):

what about concurrent changes to your object?

• user A opens the page - data is read from em1 and displayed


• while user A is still working on the object, user B also opens the same object, edits it and saves it: now it has changed in the database


• user A is now ready and calls your update method, which uses em2 to find the object

but this object now is not what you expect!
it already includes the changes of user b when you do the comparision. but as I understood: you expect the object to be what user A saw when she opened the page

note: in this case user A will get an optimistic locking exception by hibernate so she can't update the object anyway.