How to deal with subj?

Identity is available after insert only, so in order to insert details, i need apply master previously.

But i have already set details, because value object returned from UI is populated! So, calling save on it will produce exception.

If there any elegant way to handle that problem?

How about dynamic changing of association?
It it thread safe?

What i wanna do is, temporary delete cascade from master, save it, then restore it back, and save again. At this point master will have id.