Default value for foreign key in Django migrations.AddField

You can't do it directly. The recommended way of doing this is to create a migration to add it with null=True, then add a data migration that uses either Python or SQL to update all the existing ones to point to available_state_id, then a third migration that changes it to null=False.

I just had the same issue and stumbled upon this answer, so here is how I did it:

  operations = [        # We are forced to create the field as non-nullable before        # assigning each Car to a Brand        migrations.AddField(            model_name="car",            name="brand",            field=models.ForeignKey(                null=True,                on_delete=django.db.models.deletion.PROTECT,                to="model.Brand",            ),        ),        # assign_car_to_brand loops over all my Car objects and sets their        # "brand" field        migrations.RunPython(add_category_to_tags, do_nothing),        # Make the field non-nullable to force all future Car to have a Brand        migrations.AlterField(            model_name="car",            name="brand",            field=models.ForeignKey(                null=False,                on_delete=django.db.models.deletion.PROTECT,                to="model.Brand",            ),            preserve_default=False        ),    ]