FastAPI + GraphQL getting error NoneType is callable when raise Exception - graphql

Question

I'm stuck when trying to raise a validation error with FastAPI + GraphQL (graphene).
I have a resolver code:
class Query(graphene.ObjectType):
list_categories = graphene.List(CategoryGrapheneModel)
get_category = graphene.Field(CategoryGrapheneModel, id=graphene.Argument(graphene.Int, required=True))
#staticmethod
def resolve_list_categories(parent, info):
return Category.all()
#staticmethod
def resolve_get_category(parent, info, id):
try:
category = Category.find_or_fail(id)
return category
except ModelNotFound as ex:
raise Exception('Category not found')
But instead of getting 400 HTTP response with the message I got 500 Internal Server Error with traceback:
Traceback (most recent call last):
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/uvicorn/protocols/http/h11_impl.py", line 394, in run_asgi
result = await app(self.scope, self.receive, self.send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/uvicorn/middleware/proxy_headers.py", line 45, in __call__
return await self.app(scope, receive, send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/fastapi/applications.py", line 199, in __call__
await super().__call__(scope, receive, send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/applications.py", line 111, in __call__
await self.middleware_stack(scope, receive, send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/middleware/errors.py", line 181, in __call__
raise exc from None
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/middleware/errors.py", line 159, in __call__
await self.app(scope, receive, _send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/exceptions.py", line 82, in __call__
raise exc from None
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/exceptions.py", line 71, in __call__
await self.app(scope, receive, sender)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/routing.py", line 566, in __call__
await route.handle(scope, receive, send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/routing.py", line 227, in handle
await self.app(scope, receive, send)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/graphql.py", line 52, in __call__
response = await self.handle_graphql(request)
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/graphql.py", line 105, in handle_graphql
[format_graphql_error(err) for err in result.errors]
File "/Users/vitalyradchik/Devel/upwork/tipolim/backend/.venv/lib/python3.9/site-packages/starlette/graphql.py", line 105, in <listcomp>
[format_graphql_error(err) for err in result.errors]
TypeError: 'NoneType' object is not callable
Googling is not gives me a solution. So please help.

Answer 1

Got handled with it.
The problem was in GraphQLApp, there was calling format_graphql_errors that was undefined (None).
To solve a problem I've created a custom child class from GraphQLApp and changed format_graphql_errors to format_error from graphql.error.graphql_error package.
import json
import typing
from starlette.graphql import GraphQLApp
from starlette import status
from starlette.background import BackgroundTasks
from starlette.concurrency import run_in_threadpool
from starlette.requests import Request
from starlette.responses import HTMLResponse, JSONResponse, PlainTextResponse, Response
from starlette.types import Receive, Scope, Send
from graphql.error.graphql_error import format_error
class CustomGraphQLApp(GraphQLApp):
async def handle_graphql(self, request: Request) -> Response:
if request.method in ("GET", "HEAD"):
if "text/html" in request.headers.get("Accept", ""):
if not self.graphiql:
return PlainTextResponse(
"Not Found", status_code=status.HTTP_404_NOT_FOUND
)
return await self.handle_graphiql(request)
data = request.query_params # type: typing.Mapping[str, typing.Any]
elif request.method == "POST":
content_type = request.headers.get("Content-Type", "")
if "application/json" in content_type:
data = await request.json()
elif "application/graphql" in content_type:
body = await request.body()
text = body.decode()
data = {"query": text}
elif "query" in request.query_params:
data = request.query_params
else:
return PlainTextResponse(
"Unsupported Media Type",
status_code=status.HTTP_415_UNSUPPORTED_MEDIA_TYPE,
)
else:
return PlainTextResponse(
"Method Not Allowed", status_code=status.HTTP_405_METHOD_NOT_ALLOWED
)
try:
query = data["query"]
variables = data.get("variables")
operation_name = data.get("operationName")
except KeyError:
return PlainTextResponse(
"No GraphQL query found in the request",
status_code=status.HTTP_400_BAD_REQUEST,
)
background = BackgroundTasks()
context = {"request": request, "background": background}
result = await self.execute(
query, variables=variables, context=context, operation_name=operation_name
)
error_data = (
[format_error(err) for err in result.errors]
if result.errors
else None
)
response_data = {"data": result.data}
if error_data:
response_data["errors"] = error_data
status_code = (
status.HTTP_400_BAD_REQUEST if result.errors else status.HTTP_200_OK
)
return JSONResponse(
response_data, status_code=status_code, background=background
)
I hope this will help others.

Answer 2

Based on the great answer from #Vitaly Radchik, I created more universal and compressed code by redefining the existing handle_graphql after format_graphql_error is defined.
import json, typing, inspect
from starlette import status
from starlette.background import BackgroundTasks
from starlette.requests import Request
from starlette.responses import JSONResponse, PlainTextResponse, Response
from graphql.error.graphql_error import format_error as format_graphql_error
# Get source of `handle_graphql` function
code = inspect.getsource(GraphQLApp.handle_graphql).lstrip()
class CustomGraphQLApp(GraphQLApp):
# Redefine handle_graphql function
exec(code)