Django 1 7 Makemigration non-nullable field

Question

I am trying to use django-orderedmodel in my project.

But, Running makemigrations doesn't work and it shows the following:

 You are trying to add a non-nullable field 'order' to slide without a default; we can't do that (the database needs something to populate existing rows).
Please select a fix:
 1) Provide a one-off default now (will be set on all existing rows)
 2) Quit, and let me add a default in models.py
Select an option:
 

Can anyone tell me what should I do to fix this?

Answer 1

As the order field is unique, you'll need to add the field in several migration steps, replacing the original operations in your migration:

Add a nullable field, set the default to NULL.
Set the field to a unique value in each row.
Add a NOT NULL constraint.
 

You can use something like this:

operations = [
    migrations.AddField('myapp.MyModel', 'order', models.PositiveIntegerField(null=True, unique=True)),
    migrations.RunPython(set_order),
    migrations.AlterField('myapp.MyModel', 'order', models.PositiveIntegerField(blank=True, unique=True)),
]