How to make an order_with_respect_to migration work.

0005_blah.py

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

from django.db import models, migrations


class AlterOrderWithRespectTo(migrations.AlterOrderWithRespectTo):
    """
    Represents a change with the order_with_respect_to option.
    """

    def database_forwards(self, app_label, schema_editor, from_state, to_state):
        from_model = from_state.render().get_model(app_label, self.name)
        to_model = to_state.render().get_model(app_label, self.name)
        if self.allowed_to_migrate(schema_editor.connection.alias, to_model):
            # Remove a field if we need to
            if from_model._meta.order_with_respect_to and not to_model._meta.order_with_respect_to:
                schema_editor.remove_field(from_model, from_model._meta.get_field_by_name("_order")[0])
            # Add a field if we need to (altering the column is untouched as
            # it's likely a rename)
            elif to_model._meta.order_with_respect_to and not from_model._meta.order_with_respect_to:
                field = to_model._meta.get_field_by_name("_order")[0]
                field.default = 1 # !!! Added this so that no null fields are created.
                schema_editor.add_field(
                    from_model,
                    field,
                )


class Migration(migrations.Migration):

    dependencies = [
        ('listingapp', '0004_auto_20141112_1744'),
    ]

    operations = [
        AlterOrderWithRespectTo(
            name='listitem',
            order_with_respect_to='list',
        ),
    ]

Explanation.md

When I added order_with_respect_to Meta option to my model in Django 1.7, the migrations barfed. Typical makemigrations then migrate and then I got this error: django.db.utils.IntegrityError: column "_order" contains null values

Shit. After hunting around I decided to just modify how the migration was done. I subclassed the AlterOrderWithRespectTo migration and overrode the database_forwards method. It's entirely copy-paste except for line 23. The new field created in lines 22-27 is not-null but no default is provided. Barf. I added line 23 and set a default at least for the migration.