Defining a pass-through type

[patrick91]

Hi folks, here I am with another question 😊 Excuse me for the title, not sure it makes sense :)

In Strawberry we have a class called Private that can be used to annotate some fields, it works similarly to
dataclasses' InitVar, here's an example:

import strawberry

@strawberry.type
class User:
    name: str
    age: strawberry.Private[int]

patrick = User(name="Patrick", age=1)
reveal_type(patrick.age)

unfortunately this breaks the type checkers since patrick.age is Private :)

For MyPy we made a plugin to prevent this problem, is there a way to make this class a pass through to the passed type?

The only alternative I'm thinking of is to convert the class to be a function that returns typing.Annotated, but I wonder if there's a better alternative :)

Here's our implementation:

class Private:
    __slots__ = ("type",)

    def __init__(self, type):
        self.type = type

    def __repr__(self):
        if isinstance(self.type, type):
            type_name = self.type.__name__
        else:
            # typing objects, e.g. List[int]
            type_name = repr(self.type)
        return f"strawberry.Private[{type_name}]"

    def __class_getitem__(cls, type):
        return Private(type)

[erictraut]

Another option is to adopt something similar to the dataclass field descriptor function. This is a pattern that attrs, pydantic and other libraries use as well, so it's a well-trodden path.

It would look something like this:

@strawberry.type
class User:
    name: str
    age: int = strawberry.field(private=True)

(One potential problem with strawberry.field is that it might invite a copyright infringement lawsuit from the Beatles. ;) )

This approach would also work with dataclass transform.

[patrick91]

@erictraut thanks for the answer! we already have strawberry.field but we'd like to have a different syntax, I'll experiment with typing.Annotated and see if I can get something working ^^

[patrick91]

I solved this with annotated and getting rid of the custom type!

[patrick91]

I solved with Private = Annotated[T, StrawberryPrivate()] ^^

https://github.com/strawberry-graphql/strawberry/pull/1437/files