django.db.utils.IntegrityError: column “venue_city” contains null values

Question

I have read a lot of other posts here on stackoverflow and google but I could not find a solution.

It all started when I changed the model from a CharField to a ForeignKey. The error I recieve is:

Operations to perform:
  Synchronize unmigrated apps: gis, staticfiles, crispy_forms, geoposition, messages
  Apply all migrations: venues, images, amenities, cities_light, registration, auth, admin, sites, sessions, contenttypes, easy_thumbnails, newsletter
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states... DONE
  Applying venues.0016_auto_20160514_2141...Traceback (most recent call last):
  File "/Users/iam-tony/.envs/venuepark/lib/python3.4/site-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.IntegrityError: column "venue_city" contains null values

My model is as follows:

class Venue(models.Model):
    venue_city = models.ForeignKey(City, null=True,)
    venue_country=models.ForeignKey(Country, null=True)

venue_country did not exist before so that migration happened successfully. But venue_city was a CharField.

I made some changes to my migration file so that it would execute the sql as follows:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('venues', '0011_venue_map_activation'),
    ]

    migrations.RunSQL(''' ALTER TABLE venues_venue ALTER venue_city TYPE integer USING  venue_city::integer '''),

    migrations.RunSQL(''' ALTER TABLE venues_venue ALTER venue_city RENAME COLUMN venue_city TO venue_city_id '''),

    migrations.RunSQL(''' ALTER TABLE venues_venue ADD CONSTRAINT venues_venus_somefk FOREIGN KEY (venue_city_id) REFERENCES  cities_light (id) DEFERRABLE INITIALLY DEFERRED'''),

Thanks in advance!

UPDATE: my new migration file:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import migrations, models


class Migration(migrations.Migration):

    dependencies = [
        ('cities_light', '0006_compensate_for_0003_bytestring_bug'),
        ('venues', '0024_remove_venue_venue_city'),
    ]

    operations = [
        migrations.AddField(
            model_name='venue',
            name='venue_city',
            field=models.ForeignKey(null=True, to='cities_light.City'),
        ),
    ]

Answer 1

Looks like you added null=True after created migration file. Because venue_city is not a nullable field in your migration file

Follow these steps.

1) Drop venue_city & venue_country from your local table
3) Delete all the migration files you created for these `CharField to a ForeignKey` change
4) execute `python manage.py makemigrations`
5) execute 'python manage.py migrate'

It should work

Answer 2

Had a similar problem i resolved it by removing the previous migration files.No technical explanation

Answer 3

I solved it by just adding null = True to both the (automatically generated) migration file that was causing the issue and in the Model. Then migrate again and your failed migration will now succeed. As you changed it also in your model, makemigration will detect no changes after that.