Django change an existing field to foreign key

Question

I have a Django model that used to look like this:

class Car(models.Model):
    manufacturer_id = models.IntegerField()

There is another model called Manufacturer that the id field refers to. However, I realized that it would be useful to use Django's built-in foreign key functionality, so I changed the model to this:

class Car(models.Model):
    manufacturer = models.ForeignKey(Manufacturer)

This change appears to work fine immediately, queries work without errors, but when I try to run migrations, Django outputs the following:

- Remove field manufacturer_id from car
- Add field manufacturer to car

Doing this migration would clear all the existing relationships in the database, so I don't want to do that. I don't really want any migrations at all, since queries like Car.objects.get(manufacturer__name="Toyota") work fine. I would like a proper database foreign key constraint, but it's not a high priority.

So my question is this: Is there a way to make a migration or something else that allows me to convert an existing field to a foreign key? I cannot use --fake since I need to reliably work across dev, prod, and my coworkers' computers.

Answer 1

You can do data migration

1. add new field
2. do a data migration https://docs.djangoproject.com/en/3.1/topics/migrations/#data-migrations
3. remove old field

I am not sure, there might be another solution where you can rename the field to name you want to, then alter the filed to new type (do a migration)

operations = [
        migrations.RenameField(
            model_name='car',
            old_name='manufacturer_id',
            new_name='manufacturer',
        ),
        migrations.AlterField(
            model_name='car',
            name='manufacturer',
            field=ForeignKey(blank=True, null=True,  
                  on_delete=django.db.models.deletion.CASCADE
            ),
    ]