Django migration with uuid field generates duplicated values

Question

I have a uuid field (not a primary key). The generated migration is:

from __future__ import unicode_literals  from django.db import migrations, models import uuid   class Migration(migrations.Migration):      dependencies = [         ....     ]      operations = [         ...         migrations.AddField(             model_name='device',             name='uuid',             field=models.UUIDField(default=uuid.uuid4, unique=True),         ),         ...     ] 

But when doing python manage.py migrate it is crashing with:

django.db.utils.IntegrityError: could not create unique index "restaurants_device_uuid_key" DETAIL: Key (uuid)=(f3858ded-b8e0-4ac0-8436-8a61b10efc73) is duplicated.

Strangely enough, the problem does not seem to occur with primary keys (which are maybe created by the database, and not internally by django?)

How can I add a uuid field, and make sure that migrations work?

Answer 1

Here is an example doing everything in one single migration thanks to a RunPython call.

# -*- coding: utf-8 -* from __future__ import unicode_literals  from django.db import migrations, models import uuid   def create_uuid(apps, schema_editor):     Device = apps.get_model('device_app', 'Device')     for device in Device.objects.all():         device.uuid = uuid.uuid4()         device.save()   class Migration(migrations.Migration):      dependencies = [         ('device_app', 'XXXX'),     ]      operations = [         migrations.AddField(             model_name='device',             name='uuid',             field=models.UUIDField(blank=True, null=True),         ),         migrations.RunPython(create_uuid),         migrations.AlterField(             model_name='device',             name='uuid',             field=models.UUIDField(unique=True)         )     ]