Django-DB-Migrations: cannot ALTER TABLE because it has pending trigger events

Question

I want to remove null=True from a TextField:

-    footer=models.TextField(null=True, blank=True)
+    footer=models.TextField(blank=True, default='')

I created a schema migration:

manage.py schemamigration fooapp --auto

Since some footer columns contain NULL I get this error if I run the migration:

django.db.utils.IntegrityError: column "footer" contains null values

I added this to the schema migration:

    for sender in orm['fooapp.EmailSender'].objects.filter(footer=None):
        sender.footer=''
        sender.save()

Now I get:

django.db.utils.DatabaseError: cannot ALTER TABLE "fooapp_emailsender" because it has pending trigger events

What is wrong?

Answer 1

Every migration is inside a transaction. In PostgreSQL you must not update the table and then alter the table schema in one transaction.

You need to split the data migration and the schema migration. First create the data migration with this code:

 for sender in orm['fooapp.EmailSender'].objects.filter(footer=None):
    sender.footer=''
    sender.save()

Then create the schema migration:

manage.py schemamigration fooapp --auto

Now you have two transactions and the migration in two steps should work.