Problem

Currently, when trying to inherit from a class which was wrapped by strawberry.experimental.pydantic.type or -.input without any additional class variables with the strawberry.auto-annotation, a strawberry.experimental.pydantic.exceptions.MissingFieldsListError arises.

The reason is the check here:

if not fields_set:
    raise MissingFieldsListError(cls)

Example

example.py:

import strawberry
from strawberry import auto

from pydantic import BaseModel


class NoteModel(BaseModel):
    confidential: str  # do not expose via graphql
    headline: str
    text: str


@strawberry.experimental.pydantic.input(NoteModel)
class NoteInput:
    headline: auto
    text: auto


@strawberry.experimental.pydantic.type(NoteModel)
class Note(NoteInput):
    pass

raises

$ python3.10 example.py

Traceback (most recent call last):
  File "example.py", line 21, in <module>
    class Note(NoteInput):
  File "/venv/lib/python3.10/site-packages/strawberry/experimental/pydantic/object_type.py", line 113, in wrap
    raise MissingFieldsListError(cls)
strawberry.experimental.pydantic.exceptions.MissingFieldsListError: List of fields to copy from <class '__main__.Note'> is empty. Add fields with the `auto` type annotation

Why is...

.. all_fields=True not sufficient?

• If there are variables which you do not want to expose, see NoteModel.confidential in the example above.

.. empty inheritance desirable?

• To allow types and inputs with same variables.

.. non-empty inheritance without an auto-attribute desirable?

• To allow nested inputs and types where the types of the nested objects also differ. E.g.

@strawberry.experimental.pydantic.input(ImageModel, all_fields=True)
class ImageInput:
    pass

@strawberry.experimental.pydantic.input(ImageModel, all_fields=True)
class Image:
    pass

@strawberry.experimental.pydantic.input(NoteModel)
class NoteInput:
    headline: auto
    text: auto
    images: List[ImageInput]


@strawberry.experimental.pydantic.type(NoteModel)
class Note(NoteInput):
    images: List[Image]

Suggestions

My suggestion would be to completely remove the lines 106 and 107.
https://github.com/strawberry-graphql/strawberry/blob/main/strawberry/experimental/pydantic/object_type.py#L106-L107

This would solve above problems. Also, a conversion from pydantic to strawberry and vice-versa without the strawberry.auto-annotation is desirable to add the to_pydantic and from_pydantic-methods to a class.

If completely removing is not an option, a check whether any attributes are inherited might be an option, e.g.:

- if not fields_set:
+ inherited_fields = set(
+    name
+    for base in cls.__bases__
+    for name in getattr(base, "__annotations__", {}).keys()
+    if name not in existing_fields
+ )
+ if not fields_set and not inherited_fields:

I would love to open a PR for one of the above mentioned suggestions if you tell me which one you would prefer. :)