Changing the primary key of a model in Django

I had to change the primary key of a django model, and I wanted to create a migration for this.

The previous model was using django automatic primary key fields

I firstly changed the model to include the new uuid field, and added the id field (the old primary key), like this:

    uuid = models.UUIDField(
        unique=True, primary_key=True, default=uuid.uuid4, editable=False
    )
    id = models.IntegerField(null=True, blank=True)

Then I create the migration, they:

Create a new uuid field/column in the database
Iterate over the existing items in the table, to generate an uuid for them
Update the eventual references to the model so that it continues to work
Change the old primary key to a different type
Drop the old index
Mark the new primary key as such

To generate the migrations I did django-admin makemigrations, and iterated on it. Here is the migration I ended up with:

import uuid

from django.db import migrations, models

# This is done in pure python, but can probably be faster with SQL queries directly
# for a large database.
def gen_uuid(apps, schema_editor):
    DataLayer = apps.get_model("umap", "DataLayer")
    for row in DataLayer.objects.all():
        row.uuid = uuid.uuid4()
        row.save(update_fields=["uuid"])


class Migration(migrations.Migration):
    dependencies = [
        ("umap", "0017_migrate_to_openstreetmap_oauth2"),
    ]

    operations = [
        migrations.AddField(
            model_name="datalayer",
            name="uuid",
            field=models.UUIDField(default=uuid.uuid4, editable=False, null=True),
        ),
        migrations.RunPython(gen_uuid, reverse_code=migrations.RunPython.noop),
        migrations.RunSQL(
            "ALTER TABLE umap_datalayer DROP CONSTRAINT umap_datalayer_pkey"
        ),
        migrations.AlterField(
            "datalayer", name="id", field=models.IntegerField(null=True, blank=True)
        ),
        migrations.AlterField(
            model_name="datalayer",
            name="uuid",
            field=models.UUIDField(
                default=uuid.uuid4, editable=False, unique=True, primary_key=True
            ),
        ),
    ]

#django , #orm , #migrations - Posté dans la catégorie code