id	summary	reporter	owner	description	type	status	component	version	severity	resolution	keywords	cc	stage	has_patch	needs_docs	needs_tests	needs_better_patch	easy	ui_ux
29790	"Migration that switches a model to a UUID primary key fails with ""duplicate column name: id"""	Richard Ebeling	nobody	"We migrated a model from a AutoField as id (default behaviour) to a UUIDField in the past, using a migration that looked like this with django 2.0:
https://gist.github.com/smcoll/8bb867dc631433c01fd0

There was a bug in SQLite though, which as of today only has the workaround listed in the bug tracker: #28541

Thus, we ended up writing our migration like this: https://github.com/fsr-itse/EvaP/blob/master/evap/evaluation/migrations/0062_replace_textanswer_id_with_uuid.py

When we try updating to django 2.1 now, this migration fails whenever you call migrate with the error
{{{django.db.utils.ProgrammingError: multiple primary keys for table ""evaluation_textanswer"" are not allowed}}}

This commit changed the behavior: 02365d3f38a64a5c2f3e932f23925a381d5bb151

It works if we add a RemoveField instruction for the old id before setting {{{primary_key=True}}} on the new UUIDField. But this will trigger the SQLite bug listed above. Changing the old AutoField to {{{primary_key=False}}} where the RemoveField instruction would be doesn't fix the error.

The documentation states that [https://docs.djangoproject.com/en/stable/ref/models/fields/#django.db.models.Field.primary_key an object may not have more than one primary key].

Still, in the release notes for django 2.1 it should be noted that django's behavior was changed here. Also, I would appreciate if there was some kind of documentation on how you should migrate primary keys from a field to another if no two primary keys are allowed in between. There should be a way without squashing the migrations as we want to keep the history.

We are running postgres version 9.6.9 and psycopg2-binary version 2.7.5.
The migration error will not occur when using a SQLite database."	Bug	new	Migrations	2.1	Normal		multiple primary keys migration id uuid	karyon Richard Ebeling Tim Martin Ülgen Sarıkavak	Accepted	0	0	0	0	0	0