Add the ability to use a custom backend.

README.md

@@ -48,6 +48,7 @@ gql_view(request)  # <-- the instance is callable and expects a `aiohttp.web.Req
 -   `encoder`: the encoder to use for responses (sensibly defaults to `graphql_server.json_encode`)
 -   `error_formatter`: the error formatter to use for responses (sensibly defaults to `graphql_server.default_format_error`)
 -   `enable_async`: whether `async` mode will be enabled.
+-   `backend`: the backend to be used to create `GraphQLDocument` from a string (sensibly defaults to `graphql.backend.core.GraphQLCoreBackend`).
 
 
 ## Testing

aiohttp_graphql/graphqlview.py

@@ -36,6 +36,7 @@ def __init__(
             encoder=None,
             error_formatter=None,
             enable_async=True,
+            backend=None,
         ):
         # pylint: disable=too-many-arguments
         # pylint: disable=too-many-locals
@@ -58,6 +59,7 @@ def __init__(
             self.executor,
             AsyncioExecutor,
         )
+        self.backend = backend
         assert isinstance(self.schema, GraphQLSchema), \
             'A Schema is required to be provided to GraphQLView.'
 
@@ -141,6 +143,7 @@ async def __call__(self, request):
                 context_value=self.get_context(request),
                 middleware=self.middleware,
                 executor=self.executor,
+                backend=self.backend,
             )
 
             awaited_execution_results = await Promise.all(execution_results)