cubicweb #2981599 unique constraint and yams inheritance [open]

given the following schema:

class Workcase(EntityType):
  ref = String(unique=True)

class Training(Workcase):
  __specializes_schema__ = True

One could expect that ref are unique accross both trainings and workcases. This is currently not the case, they are unique among each type separatly, and one have to setup a RQLUniqueConstraint if he want shared refs.

We may want to keep this behaviour but it should be documented.

done in<not specified>
closed by<not specified>