[ubernostrum]

Django's ORM will create DB-level foreign keys on databases/table engines that support them. But it doesn't create many other types of database-level validation (mostly just UNIQUE and NOT NULL constraints).

Some of that is compatibility reasons; not every DB Django supports would allow creating all the desired types of constraints in the DB, so Django has no choice but to ship application-layer enforcement.

You can work around that with manually-created migrations (and I've worked some places that did this, in order to get particular constraint types that were needed at the DB level), but I don't know of a good generic solution to that problem.

Django 2.2 is going with a somewhat-manual approach to allow specifying richer types of constraints, so maybe that'll lead to progress.