example model:

Building

v 0..*
Flat <<abstract>>
^

----------

Loft Suite

The unit test will throw an exception:

ERROR: Table "FLAT" not found; SQL statement:
update Flat set building=?, building_idx=? where flatId=? [42102-177]

This is due to used of union-subclass, in that case indexes have to be created on concrete entities tables as Loft and Suite
and not Flat for this example.