Update migration when adding uuids

reference: https://docs.djangoproject.com/en/dev/howto/writing-migrations/#migrations-that-add-unique-fields

backend/api/migrations/0017_example_uuid.py

@@ -9,7 +9,7 @@ def create_uuid(apps, schema_editor):
     Example = apps.get_model("api", "example")
     for example in Example.objects.all():
         example.uuid = uuid.uuid4()
-        example.save()
+        example.save(update_fields=["uuid"])
 
 
 class Migration(migrations.Migration):
@@ -24,6 +24,8 @@ class Migration(migrations.Migration):
             name="uuid",
             field=models.UUIDField(editable=False, blank=True, null=True),
         ),
-        migrations.RunPython(create_uuid),
-        migrations.AlterField(model_name="example", name="uuid", field=models.UUIDField(db_index=True, unique=True)),
+        migrations.RunPython(create_uuid, reverse_code=migrations.RunPython.noop),
+        migrations.AlterField(
+            model_name="example", name="uuid", field=models.UUIDField(default=uuid.uuid4, db_index=True, unique=True)
+        ),
     ]