(0.16.14) Cyclic FK References

I have 2 models: User and FileAttachment.

User is John Doe User uploads a random file, he becomes the owner of that FileAttachment using a ‘created_by’ field on the FileAttachment I try to add a ‘avatar’ field on the User object that’s a foreignkey reference to FileAttachment, I get the cyclic fk error.

class User(Model):
    first_name = fields.CharField(max_length=255, null=False)
    last_name = fields.CharField(max_length=255, null=False)
    picture = fields.ForeignKeyField('models.FileAttachment')

class FileAttachment(Model):
    created_by = fields.ForeignKeyField('models.User', related_name='files')

  File "py", line 46, in init_tortoise
    await Tortoise.generate_schemas()
  File "/Users/phil/.pyenv/versions/lib/python3.8/site-packages/tortoise/__init__.py", line 596, in generate_schemas
    await generate_schema_for_client(connection, safe)
  File "/Users/phil/.pyenv/versions/lib/python3.8/site-packages/tortoise/utils.py", line 29, in generate_schema_for_client
    schema = get_schema_sql(client, safe)
  File "/Users/phil/.pyenv/versions/lib/python3.8/site-packages/tortoise/utils.py", line 18, in get_schema_sql
    return generator.get_create_schema_sql(safe)
  File "/Users/phil/.pyenv/versions/lib/python3.8/site-packages/tortoise/backends/base/schema_generator.py", line 408, in get_create_schema_sql
    raise ConfigurationError("Can't create schema due to cyclic fk references")
tortoise.exceptions.ConfigurationError: Can't create schema due to cyclic fk references

If I make the changes directly in Postgres, it accepts them. It’s only tortoise that seems to dislike it 😃

[zikphil]

Oh sorry I missed the thread here. I don’t think it’s a question of good or bad model design. Sounds more like a software limitation 😛 A user field on each model for created_by is pretty standard. To follow this logic I would have to create a new table/model for avatars instead of using my File object, which is what I ended up doing but It felt a big wrong to just duplicate objects to counter the limitation.

[lesywix]

I also meet this problem when I’m doing migration using aerich (It’ll use the tortoise generate schema to init db).

My solution is to remove Tortoise.generate_schemas() to make sure the FastAPI can works. For the migration, I temporarily remove the cyclic FKs on one model to make sure the aerich can init-db successful, then add the cyclic FKs back manually to generate the FKs.