ForeignKey on_delete functionality should traverse (cascade, ha ha) to the DB backend
|Reported by:||gcbirzan||Owned by:||nobody|
|Component:||Database layer (models, ORM)||Version:||master|
|Has patch:||no||Needs documentation:||no|
|Needs tests:||no||Patch needs improvement:||no|
By default, django creates FKs without an explicit ON DELETE on the backend. This, if nothing else, should be configurable. If for no other reason that when using some transaction isolation modes, the error returned by the backend will be the wrong one during concurrent modifications:
Table b links to table a. You insert in table b a link to ID 1 in a, at the same time as you delete it from a.
With the default (at least in PostgreSQL), in REPEATABLE READ, the error is IntegrityError, which is wrong, since in fact you should just retry the transaction. In lower isolation levels, the FK is deleted (as expected), though, granted the on delete signals are not called.