strawberry.Parent not supporting forward refs

[andrewkruse]

I would like the strawberry documentation on accessing parent with function resolvers on this page tweaked to be more clear, or maybe corrected?

From what I understand in the docs, its suggesting you end up with the following. However, this doesn't even run? I have tried swapping the definitions both directions, they have the same issue. I had to resort to the self method on a method resolver, which seems less desirable to me since the docs specifically call out that it might not work quite right everywhere.

and it works like it should in Python, but there might be cases where it doesn’t properly follow Python’s semantics

def get_full_name(parent: strawberry.Parent[User2]) -> str:
    return f"{parent.first_name} {parent.last_name}"

@strawberry.type
class User2:
    first_name: str
    last_name: str
    full_name: str = strawberry.field(resolver=get_full_name)

Traceback (most recent call last):
  File "/Users/.../Library/Application Support/JetBrains/IntelliJIdea2024.1/plugins/python/helpers/pydev/pydevd.py", line 1535, in _exec
    pydev_imports.execfile(file, globals, locals)  # execute the script
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../Library/Application Support/JetBrains/IntelliJIdea2024.1/plugins/python/helpers/pydev/_pydev_imps/_pydev_execfile.py", line 18, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "/Users/.../src/api/python-graphql-poc/src/main.py", line 21, in <module>
    def get_full_name(parent: strawberry.Parent[User2]) -> str:
                                                ^^^^^
NameError: name 'User2' is not defined

Perhaps there's a quirk in here where the structure of my file is part of the problem since everything is top level? I am using FastAPI, uvicorn and strawberry.

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[patrick91]

@andrewkruse I think you found a bug, this should work:

from __future__ import annotations   # NOTE: this

import strawberry


def get_full_name(user: strawberry.Parent[User]) -> str:
    return f"{user.first_name} {user.last_name}"


@strawberry.type
class User:
    first_name: str
    last_name: str
    full_name: str = strawberry.field(resolver=get_full_name)


@strawberry.type
class Query:
    @strawberry.field
    def user(self) -> User:
        return User(first_name="John", last_name="Doe")


schema = strawberry.Schema(query=Query)

but it doesn't work

[caspervk]

Any updates on this? I don't understand how strawberry.Parent can be used with self-referential types in its current form.

cc: @mattalbr as original strawberry.Parent implementer in #3017.

[mattalbr]

Great question @caspervk and sorry for the bad documentation! Here's some code grabbed directly from my company's repository that is running:

@strawberry.type
class Foo:

    @strawberry.field
    @staticmethod
    async def bar(
        foo: strawberry.Parent[Annotated["Foo", strawberry.lazy(".foo")]], info: types.Info
    ) -> str | None:
        pass

It's unfortunately mad verbose, but the challenge is that we need to have the resolver defined before we've even finished defining the strawberry.type, so we need a forward declaration of sorts. Patrick might be able to find a more clever succinct definition, but this is what we've been using so far.

If that solves your problem, let me know, and I can send out a PR updating the docs.

[caspervk]

Thank you! It works! 👑 I didn't even think of using strawberry.lazy since everything is in the same file. It seems very-slightly-less verbose strawberry.Parent[Annotated["Foo", strawberry.lazy(".")]] also works in that case.

[tokarenko]

@mattalbr, please advise why I am unable to get this working for the Query object. The reference (parent) is always None. I am at version 0.237.3.

@strawberry.type
class Query:
    repository: strawberry.Private[Repository]

    @strawberry.field
    @staticmethod
    def vrf(
        parent: strawberry.Parent[Annotated["Query", strawberry.lazy(".")]],
        ...
    ) -> List[VRFType]:
        ...

[mattalbr]

Hi @tokarenko -- it's hard to tell from just that snippet, but based on your class being called "Query" I'm assuming that's the top level query class for your schema. If so, you'll need to pass the root value in when you call schema.execute.

https://strawberry.rocks/docs/types/schema#root_value-optionalany--none

If the value is present when you name the field "root" and not when you use the strawberry.Parent annotation, that would be a bug that we should address. I went back through the original PR in #3017 and it looks like I missed test coverage for that specific case, but I would expect the code to work -- please let us know it if doesn't!

[tokarenko]

@mattalbr , thank you for the instructions. It works. When the top level Query class is added to schema.execute as root_value, it gets passed either as argument named root or as argument with strawberry.Parent annotation. Please consider documenting this as it is not straightforward and/or setting default for root_value to schema.query.