Best practice for Save&Cancel dialog with associated objects

Hi all,

I quite often stumble across the following 'standard problem' for modeling an edit/new dialog.

I have this domain model:

So, essentially a Category has a n:m relation to a Person with an attribute PersonRole.

Now when I start with the New and Edit dialogue I end up with this design:

In the dialog I want to change the Category name and add/delete Persons from the category.

Now the problem is: how can you get the Add and Delete functions to properly work with the Save and Cancel Buttons (i.e. Cancel should roll back ALL changes, and no changes are persisted until pressing Save).

I would really like to read how others solve this problem with minimal effort.

regards, Fabian