Can't delete data file type that is referenced from item subtype

[Nicklas Nordborg]

We have an item subtype and a data file type. The item subtype has been configured with a reference to the data file type.

When trying to delete the data file type there is no indication that it is used in the trashcan. This results in the following exception:

update or delete on table "DataFileTypes" 
violates foreign key constraint "FKmnjqbi7ofj7k0bam7cyh5t3k5" 
on table "ItemSubtypeFileTypes"
Detail: Key (id)=(204867) is still referenced from table "ItemSubtypeFileTypes".

The workaround is to manually remove the link between the item subtype and the data file type. This is done from the item subtype edit dialog.