django model AutoField error - django

Question

I had a model like this
class Alrule(models.Model):
priority = models.PositiveIntegerField(unique=True)
rule = models.CharField(max_length=256)
I migrated this model. After I decided to make priority field as primary key with AutoField
Then my model looked like this:
class Alrule(models.Model):
priority = models.AutoField(primary_key=True)
rule = models.CharField(max_length=256)
I made a migration and migrated this change.
Now again i needed to revert back. Now I made following changes:
class Alrule(models.Model):
priority = models.PositiveIntegerField(unique=True)
rule = models.CharField(max_length=256)
I made a migration.
Now when I migrate I get the following ERROR:
AssertionError: A model can't have more than one AutoField.
My understanding is priority field was set to AutoField before and it is not removed. Please help
My first migration look like this:
operations = [
migrations.RemoveField(
model_name='alrule',
name='id',
),
migrations.AlterField(
model_name='alrule',
name='priority',
field=models.AutoField(serialize=False, primary_key=True),
),
]
Second migration looks like this:
operations = [
migrations.AddField(
model_name='alrule',
name='id',
field=models.AutoField(auto_created=True, primary_key=True, default=2, serialize=False, verbose_name='ID'),
preserve_default=False,
),
migrations.AlterField(
model_name='alrule',
name='priority',
field=models.PositiveIntegerField(unique=True),
),
]

Answer 1

If you use mssql-django, there is some limitations:
The following features are currently not supported:
mssql-django does not support SQL-based regex commands
Altering a model field from or to AutoField at migration
https://github.com/microsoft/mssql-django#limitations

Answer 2

operations = [
migrations.AddField(
model_name='alrule',
name='id',
field=models.AutoField(auto_created=True, primary_key=True, default=2, serialize=False, verbose_name='ID'),
preserve_default=False,
),
migrations.AlterField(
model_name='alrule',
name='priority',
field=models.PositiveIntegerField(unique=True),
),
]
Your table already has AutoField and with first operation you are adding another one.
To avoid that just swap your operations in your migration like this:
operations = [
migrations.AlterField(
model_name='alrule',
name='priority',
field=models.PositiveIntegerField(unique=True),
),
migrations.AddField(
model_name='alrule',
name='id',
field=models.AutoField(auto_created=True, primary_key=True, default=2, serialize=False, verbose_name='ID'),
preserve_default=False,
),
]
I.e. first alter field (remove AutoField from table) and after that is done - add your id AutoField back.

Answer 3

That is because AutoField has not been removed just as you correctly indicated. Delete these two migration files and run makemigrations again. If it doesn't work, you might have to also delete the migration file before that and run migrations again.
As a last resort, you could just delete the migrations files apart from the init.py file. But then, I am sure it should work once you delete these two migrations and make a new migration from there.

Answer 4

Yes I got the simple hack of the problem. It is like this
Make the final change like this:
class Alrule(models.Model):
prioriti = models.PositiveIntegerField(unique=True)
rule = models.CharField(max_length=256)
Here priority field should be given new name ('prioriti') so that previos one gets deleted completely and a new field is created.
Now make and apply migrations.
Now again rename "prioriti" field back to "priority". And make and apply migration.
And we are done.