add database constraint between fs_betrieb and fs_betrieb_kategorie
It is required to adjust the current implementation of StoreModel.php so that NULL instead of 0 is written to the database field fs_betrieb.betrieb_kategorie_id in case that no category is selected. After that a data clean-up needs to be performed to replace existing 0 values in fs_betrieb.betrieb_kategorie_id with NULL before the constraint can be established.
Edited by Guenter Muehldorfer