Thx. That worked. The groupby works now as a charm - even if it might involve creating a complete in memory list. But that has to be done anyways-
Another problem you might help out - as I am not sure how the system is working here.
It seems that the b objects are stored in the database table b, when I store the objects for "a". Is that correct?
But the deserialisation of a will somehow lead to an empty a.liste collection. Is the sub-object not retrieved/stored? How would I do that? Store only the b-related e a.liste objects?