Currently, we need to set the default value to strawberry.arguments.UNSET to support optional arguments. This object has the Any annotation which hides itself from type checkers.

Example:

id: Optional[strawberry.ID] = UNSET

MyPy will consider id to be a Union[ID, None] while in reality, it's a Union[ID, None, _Unset]. This results in potential bugs in code where the type-checker would catch it.

For example, the following snippet will raise an error without a type checker catching it:

def foo(id: Optional[str] = UNSET) -> None:
  if id is not None:
    print(id.lower()) # Will attempt to call `lower()` on `UNSET`

Proposal

My proposal is to introduce a new type alias as a first-class citizen in the Strawberry type system:

T = TypeVar("T")
UnsetOrOptional = Union[_Unset, Optional[T]]

And its usage in resolvers:

@strawberry.field
def foo(id: UnsetOrOptional[strawberry.ID]) -> None:
  pass

• The default assignment of the arguments remain used for actual default values in GraphQL
• The body of our resolver has the current triple Union to enforce it to check for unset as well
• The upstream logic will automatically assign UNSET to its value if it was not included in the request

Just optional

This allows us to also provide the option for resolvers to define a simpler default behavior when we only care about strawberry.ID vs None:

@strawberry.field
def foo(id: Optional[strawberry.ID]) -> None:
  pass

• No default assignment needed if you don't want it to show up in the generated GraphQL schema
• The upstream logic will automatically assign None to its value if it was not included in the request