I find your pattern very 'odd', and I am too tired right now to even
try to understand how you came to this modeling decision.
If you want to limit the number of available instances, you should
simply prohibit it, either via a Constraint or by throwing an
Exception in lifecycle methods. Modifying Identity is not the way to
go, IMNSHO.
Okay, let's reverse the setting of a problem.
I have a role X with property y. I need X.y() to be unique in scope of
entity type. That means, from all entites of type Z, that have role X,
if there is some entity that has V as value of X.y(), there are no
other entites of type Z, that have same V as value of X.y(). How do I
achieve that?
One way to do this by creating life-cycle mixin, which in create()
queries all the entities of current type, having their X.y() as the
value of X.y() of current entity. If query returns any results, it
throws lifecycle-exception. This requires adding a querying service to
your app.
Another way is described in QI-272. Is that too hacky?
Are there any other ways?
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