It seems strawberry doesn't support default_factory for query arguments. Like in example below:

import json
import typing
from typing import NewType

import strawberry
from fastapi import FastAPI
from strawberry.fastapi import GraphQLRouter

data = [{"name": "A", "age": 12}, {"name": "B", "age": 20}]


@strawberry.type
class Info:
    name: str
    age: int


JSON = strawberry.scalar(
    NewType("JSON", object),
    description="The `JSON` scalar type represents JSON values as specified by ECMA-404",
    serialize=lambda v: v,
    parse_value=lambda v: v,
)


def get_data(
    where: typing.Optional[JSON] = strawberry.field(default_factory=dict), #FIXME to None
) -> typing.Optional[typing.List[Info]]:
    if where is None: result= data
    elif len(where) != 0: result = [d for d in data if d.get("name") == where.get("name")]
    else: result = data
    return json.loads(json.dumps(result), object_hook=lambda d: Info(**d))


@strawberry.type
class Query:
    informations: typing.Optional[typing.List[Info]] = strawberry.field(resolver=get_data)

schema = strawberry.Schema(query=Query)
graphql_app = GraphQLRouter(
    schema
)
app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

Here, I couldn't find a way to set where argument be dict using default_factory. Using the same code as above result in AST error unless we replace strawberry.field(default_factory=dict) or {} by None.