Error when migrating: django.db.utils.IntegrityError: column "primary_language_id" contains null values

Question

I am working on a Django project and made a model with several instances of a models.ForeignKey with the same Model.

class Country(models.Model):
    name = models.CharField(max_length=100)
    primary_language = models.ForeignKey('Language', related_name='primary_language', default="")
    secondary_language = models.ForeignKey('Language', related_name='secondary_language', default="")
    tertiary_language = models.ForeignKey('Language', related_name='tertiary_language', default="")

    def __str__(self):
        return self.name

This is the Language model:

class Language(models.Model):
    name = models.CharField(max_length=50)
    abbreviation = models.CharField(max_length=2)

    def __str__(self):
        return self.name

when doing $python3 manage.py makemigration baseit works fine, no errors. I have put the 2 migration files I think are the most important.

class Migration(migrations.Migration):

    dependencies = [
        ('base', '0002_country_country_code'),
    ]

    operations = [
        migrations.CreateModel(
            name='Currency',
            fields=[
                ('id', models.AutoField(serialize=False, auto_created=True, verbose_name='ID', primary_key=True)),
                ('name', models.CharField(max_length=50)),
                ('abbreviation', models.CharField(max_length=3)),
            ],
        ),
        migrations.CreateModel(
            name='Language',
            fields=[
                ('id', models.AutoField(serialize=False, auto_created=True, verbose_name='ID', primary_key=True)),
                ('name', models.CharField(max_length=50)),
                ('abbreviation', models.CharField(max_length=2)),
            ],
        ),
        migrations.AddField(
            model_name='country',
            name='phone_country_code',
            field=models.CharField(default='', max_length=7),
        ),
        migrations.AlterField(
            model_name='country',
            name='country_code',
            field=models.CharField(default='', max_length=2),
        ),
        migrations.AddField(
            model_name='country',
            name='primary_language',
            field=models.ForeignKey(to='base.Language', default=''),
        ),
        migrations.AddField(
            model_name='country',
            name='secondary_language',
            field=models.ForeignKey(related_name='secondary_language', to='base.Language', default=''),
        ),
        migrations.AddField(
            model_name='country',
            name='tertiary_language',
            field=models.ForeignKey(related_name='tertiary_language', to='base.Language', default=''),
        ),
    ]

class Migration(migrations.Migration):

    dependencies = [
        ('base', '0006_auto_20151023_0918'),
    ]

    operations = [
        migrations.AddField(
            model_name='country',
            name='primary_language',
            field=models.ForeignKey(default='', related_name='primary_language', to='base.Language'),
        ),
        migrations.AddField(
            model_name='country',
            name='secondary_language',
            field=models.ForeignKey(default='', related_name='secondary_language', to='base.Language'),
        ),
        migrations.AddField(
            model_name='country',
            name='tertiary_language',
            field=models.ForeignKey(default='', related_name='tertiary_language', to='base.Language'),
        ),
        migrations.AlterField(
            model_name='language',
            name='abbreviation',
            field=models.CharField(max_length=2),
        ),
        migrations.AlterField(
            model_name='language',
            name='name',
            field=models.CharField(max_length=50),
        ),
    ]

Now when running the migration I get an error message I can't figure out. I think these are the lines that matter in the stacktrace:

johan@johan-pc:~/sdp/gezelligehotelletjes_com$ python3 manage.py migrate
Operations to perform:
  Synchronize unmigrated apps: staticfiles, messages
  Apply all migrations: auth, base, sessions, admin, contenttypes, hotel
Synchronizing apps without migrations:
  Creating tables...
    Running deferred SQL...
  Installing custom SQL...
Running migrations:
  Rendering model states... DONE
  Applying base.0003_auto_20151023_0912...Traceback (most recent call last):
  File "/usr/local/lib/python3.4/dist-packages/django/db/backends/utils.py", line 64, in execute
    return self.cursor.execute(sql, params)
psycopg2.IntegrityError: column "primary_language_id" contains null values


The above exception was the direct cause of the following exception:

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

First of all I do not have a column "primary_language_id" but I guess this is created by Django. Even when deleting the entire Language model and the lines for the languages in the Country model, I still get this error.

Could someone help me with figuring this out?

Answer 1

You already have Country objects in your database.

When you add the primary_language_id column to them (which represents the primary_language ForeignKey), those countries end up with an empty primary_language (because you didn't specify a default), which throws an error (because you didn't allow empty values either for primary_language).

The solution depends on how you want that migration to work. You can add blank = True to the primary_language ForeignKey definition, add a default, or you break down your migration in 3 migrations (add the column with blank = True, set values, remove blank = True).