Change tracking API in Cayenne

Was just answering Cayenne change tracking question on StackOverlow [1], and realized that the only user-friendly API that allows to check for individual changes is "cayenne-commitlog" that only works during commit. All the pre-commit APIs are internal and require lots of hoop jumping. I think we can address that on the cheap in 4.2 by defining a method like this in GraphManager.java:

  GraphDiff getChanges();

We already have such method implemented in ObjectStore, so there's really no effort and an immediate benefit. Or take it a step further and additionally implement filtering changes per object:

  GraphDiff getChanges(Persistent)

Thoughts?

Andrus

[1] https://stackoverflow.com/questions/58318730/what-is-the-current-best-method-of-getting-the-changes-to-an-object-hierarchy-in