Typing problems with Pydantic/FastAPI integration Resolver

[invokermain]

Hi all,

I have the following set up, but the typing either doesn't play nice with type checking, or I receive type related errors when querying.

Example Application

Dependencies

Strawberry:

name = "strawberry-graphql"
version = "0.111.1"

FastAPI:

name = "fastapi"
version = "0.76.0"

MyPY

name = "mypy"
version = "0.950"

Code

import strawberry
import uvicorn
from fastapi import FastAPI
from pydantic import BaseModel
from strawberry.fastapi import GraphQLRouter


class DocumentModel(BaseModel):
    id: int
    name: str


@strawberry.experimental.pydantic.type(model=DocumentModel, all_fields=True)
class DocumentType:
    pass


def get_document(document_id: int):
    return DocumentModel(id=1, name="test")


@strawberry.type
class Query:
    document: DocumentType = strawberry.field(get_document)


schema = strawberry.Schema(Query)

graphql_app = GraphQLRouter(schema)

app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

if __name__ == "__main__":
    uvicorn.run(app, port=9000)

Result

This works as intended. However running mypy on this file (with the extension) provides the following error, unsure if it's related:

scrap.py:25: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.950
Traceback (most recent call last):
  File "C:\Program Files\Python310\lib\runpy.py", line 196, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Program Files\Python310\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "mypy\semanal.py", line 5301, in accept
  File "mypy\nodes.py", line 1021, in accept
  File "mypy\semanal.py", line 1121, in visit_class_def
  File "mypy\semanal.py", line 1201, in analyze_class
  File "mypy\semanal.py", line 1210, in analyze_class_body_common
  File "mypy\semanal.py", line 1256, in apply_class_plugin_hooks
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\ext\mypy_plugin.py", line 798, in custom_dataclass_class_maker_callback
    transformer.transform()
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\ext\mypy_plugin.py", line 476, in transform
    attributes = self.collect_attributes()
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\ext\mypy_plugin.py", line 653, in collect_attributes
    has_field_call, field_args = _collect_field_args(stmt.rvalue)
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\ext\mypy_plugin.py", line 449, in _collect_field_args
    assert name is not None

Problem

However I start running into trouble when type hinting the return of get_document and/or static type checking .

Consider the following situations

Situation 1: Adding correct Type Hint

def get_document(document_id: int) -> DocumentModel:
    return DocumentModel(id=1, name="test")

This will raise: TypeError: Query fields cannot be resolved. Unexpected type '<class '__main__.DocumentModel'>'. Even though the code is functionally identical. This is pretty strange and non-intuitive.

Mypy shows the same traceback.

Situation 2: Adding incorrect Type Hint

def get_document(document_id: int) -> DocumentType:
    return DocumentModel(id=1, name="test")

This works but break static type checking using the IDE (PyCharm).

Mypy shows the same traceback.

Situation 3: Using from_pydantic, no Type Hint

def get_document(document_id: int):
    return DocumentType.from_pydantic(DocumentModel(id=document_id, name="test"))

This works but has no typing.

Mypy shows the same traceback.

Situation 4: Using from_pydantic, with effectively correct DocumentType type hint

def get_document(document_id: int) -> DocumentType:
    return DocumentType.from_pydantic(DocumentModel(id=document_id, name="test"))

This works but break static type checking using the IDE (PyCharm).

Mypy shows the same traceback.

Situation 5: Using from_pydantic, with technically correct type hint

def get_document(document_id: int) -> StrawberryTypeFromPydantic[DocumentModel]:
    return DocumentType.from_pydantic(DocumentModel(id=document_id, name="test"))

This fails to launch with the following traceback:

Traceback (most recent call last):
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\scrap.py", line 24, in <module>
    class Query:
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\object_type.py", line 236, in type
    return wrap(cls)
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\object_type.py", line 222, in wrap
    wrapped = _wrap_dataclass(cls)
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\object_type.py", line 105, in _wrap_dataclass
    return dataclasses.dataclass(cls)
  File "C:\Program Files\Python310\lib\dataclasses.py", line 1185, in dataclass
    return wrap(cls)
  File "C:\Program Files\Python310\lib\dataclasses.py", line 1176, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
  File "C:\Program Files\Python310\lib\dataclasses.py", line 956, in _process_class
    cls_fields.append(_get_field(cls, name, type, kw_only))
  File "C:\Program Files\Python310\lib\dataclasses.py", line 766, in _get_field
    or (isinstance(f.type, str)
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\field.py", line 209, in type
    if self.base_resolver.type is not None:
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\types\fields\resolver.py", line 138, in type
    return self.type_annotation.resolve()
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\annotation.py", line 80, in resolve
    return self.create_concrete_type(evaled_type)
  File "C:\dev\gitlab\apps\web-apps\accounts-payable\src\backend\.venv\lib\site-packages\strawberry\annotation.py", line 107, in create_concrete_type
    return type_definition.resolve_generic(evaled_type)
AttributeError: 'property' object has no attribute 'resolve_generic'

Mypy shows the same traceback.

Dicussion

What is the correct Typehint for the Resolver in this situation? Feels like Situation4 is the correct one, but from_pydantic seems to have the wrong typing then?

Is the type checking only supposed to work with mypy? i.e. are IDE type warnings expected?

What's with the mypy issue? Seems like a separate bug?

Let me know if you want me to raise issues off the back of any of this, or anyone has any suggestions as to correct usage.