Django migration IntegrityError: invalid foreign key (but the data exists)

Question

I am gradually updating a legacy Django application from 1.19 -> 2.2 and beyond. To upgrade to 2.2, I just added on_delete=models.CASCADE to all models.ForeignKey fields that did not have the error (which I also had to do retroactively for existing migrations, apparently...).

Possibly related/unrelated to that, when I run manage.py migrate, Django throws the following error (I shortened the table/field names for brevity):

django.db.utils.IntegrityError: The row in table 'X' with primary key '3' has an invalid foreign key: X.fieldname_id contains a value '4' that does not have a corresponding value in Y__old.id.

Note in particular the __old.id suffix for the db table that Django expects to contain a row with id 4. When manually inspecting the db, the table Y does really contain a valid row with id 4! I'm assuming, to support the migration, Django is making some temporary tables suffixed with __old and somehow it is unable to migrate said data?

The db row Y in question is really simple: a char, boolean, and number column.

Edit: seems to be related to an old Django bug with SQLite. Not sure how to solve. It does not seem to occur for Django 2.1.15, and starts to occur in Django 2.2.

Answer 1

It is not an ideal solution, but you can manually delete the row from the database or set the value of the foreign key to a temporary value, migrate and then restore the original value.