FastAPI

Strawberry provides support for FastAPI with a custom APIRouter called GraphQLRouter .

Before using Strawberry’s FastAPI support make sure you install all the required dependencies by running:

Terminal window
pip install 'strawberry-graphql[fastapi]'

See the example below for integrating FastAPI with Strawberry: 

import strawberry


from fastapi import FastAPI
from strawberry.fastapi import GraphQLRouter




@strawberry.type
class Query:
    @strawberry.field
    def hello(self) -> str:
        return "Hello World"




schema = strawberry.Schema(Query)


graphql_app = GraphQLRouter(schema)


app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

Options

The GraphQLRouter accepts the following options:

context_getter

The context_getter option allows you to provide a custom context object that can be used in your resolver. context_getter is a FastAPI dependency and can inject other dependencies if you so wish.

There are two options at your disposal here:

  1. Define your custom context as a dictionary,
  2. Define your custom context as a class.

If no context is supplied, then the default context returned is a dictionary containing the request, the response, and any background tasks.

However, you can define a class-based custom context inline with FastAPI practice . If you choose to do this, you must ensure that your custom context class inherits from BaseContext or an InvalidCustomContext exception is raised.

For dictionary-based custom contexts, an example might look like the following. 

import strawberry


from fastapi import FastAPI, Depends, Request, WebSocket, BackgroundTasks
from strawberry.fastapi import GraphQLRouter




def custom_context_dependency() -> str:
    return "John"




async def get_context(
    custom_value=Depends(custom_context_dependency),
):
    return {
        "custom_value": custom_value,
    }




@strawberry.type
class Query:
    @strawberry.field
    def example(self, info: strawberry.Info) -> str:
        return f"Hello {info.context['custom_value']}"




schema = strawberry.Schema(Query)


graphql_app = GraphQLRouter(
    schema,
    context_getter=get_context,
)


app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

Here we are returning a custom context dictionary that contains one extra item called “customvalue”, which is injected from custom_context_dependency . This value exists alongside request , response , and background_tasks in the info.context _dictionary and so it requires ['request'] indexing.

Then we use the context in a resolver. The resolver will return “Hello John” in this case.

For class-based custom contexts, an example might look like the following. 

import strawberry


from fastapi import FastAPI, Depends, Request, WebSocket, BackgroundTasks
from strawberry.fastapi import BaseContext, GraphQLRouter




class CustomContext(BaseContext):
    def __init__(self, greeting: str, name: str):
        self.greeting = greeting
        self.name = name




def custom_context_dependency() -> CustomContext:
    return CustomContext(greeting="you rock!", name="John")




async def get_context(
    custom_context=Depends(custom_context_dependency),
):
    return custom_context




@strawberry.type
class Query:
    @strawberry.field
    def example(self, info: strawberry.Info) -> str:
        return f"Hello {info.context.name}, {info.context.greeting}"




schema = strawberry.Schema(Query)


graphql_app = GraphQLRouter(
    schema,
    context_getter=get_context,
)


app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

In this case, we are returning a custom context class that inherits from BaseContext with fields name and greeting , which is also injected by custom_context_dependency . These custom values exist alongside request , response , and background_tasks in the info.context class and so it requires .request indexing.

Then we use the context in a resolver. The resolver will return “Hello John, you rock!” in this case.

Setting background tasks

Similarly, background tasks can be added via the context: 

import strawberry


from fastapi import FastAPI, BackgroundTasks
from strawberry.fastapi import GraphQLRouter




async def notify_new_flavour(name: str):
    print(name)




@strawberry.type
class Query:
    @strawberry.field
    def hello(self) -> str:
        return "Hello World"




@strawberry.type
class Mutation:
    @strawberry.mutation
    def create_flavour(self, name: str, info: strawberry.Info) -> bool:
        info.context["background_tasks"].add_task(notify_new_flavour, name)
        return True




schema = strawberry.Schema(Query, Mutation)


graphql_app = GraphQLRouter(schema)


app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

If using a custom context class, then background tasks should be stored within the class object as .background_tasks .

root_value_getter

The root_value_getter option allows you to provide a custom root value for your schema. This is most likely a rare usecase but might be useful in certain situations.

Here’s an example: 

import strawberry


from fastapi import FastAPI
from strawberry.fastapi import GraphQLRouter




async def get_root_value():
    return Query(name="Patrick")




@strawberry.type
class Query:
    name: str




schema = strawberry.Schema(Query)


graphql_app = GraphQLRouter(
    schema,
    root_value_getter=get_root_value,
)


app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

Here we are returning a Query where the name is “Patrick”, so when we request the field name we’ll return “Patrick”.

Extending the router

The base GraphQLRouter class can be extended by overriding any of the following methods:

process_result

The process_result option allows you to customize and/or process results before they are sent to the clients. This can be useful for logging errors or hiding them (for example to hide internal exceptions).

It needs to return a GraphQLHTTPResponse object and accepts the request and execution results. 

from starlette.requests import Request
from strawberry.fastapi import GraphQLRouter
from strawberry.http import GraphQLHTTPResponse
from strawberry.types import ExecutionResult




class MyGraphQLRouter(GraphQLRouter):
    async def process_result(
        self, request: Request, result: ExecutionResult
    ) -> GraphQLHTTPResponse:
        data: GraphQLHTTPResponse = {"data": result.data}


        if result.errors:
            data["errors"] = [err.formatted for err in result.errors]


        return data

In this case we are doing the default processing of the result, but it can be tweaked based on your needs.

decode_json

decode_json allows to customize the decoding of HTTP and WebSocket JSON requests. By default we use json.loads but you can override this method to use a different decoder. 

from strawberry.fastapi import GraphQLRouter
from typing import Union
import orjson




class MyGraphQLRouter(GraphQLRouter):
    def decode_json(self, data: Union[str, bytes]) -> object:
        return orjson.loads(data)

Make sure your code raises json.JSONDecodeError or a subclass of it if the JSON cannot be decoded. The library shown in the example above, orjson , does this by default.

encode_json

encode_json allows to customize the encoding of HTTP and WebSocket JSON responses. By default we use json.dumps but you can override this method to use a different encoder. 

from strawberry.fastapi import GraphQLRouter
import json




class MyGraphQLRouter(GraphQLRouter):
    def encode_json(self, data: object) -> bytes:
        return json.dumps(data, indent=2)

render_graphql_ide

In case you need more control over the rendering of the GraphQL IDE than the graphql_ide option provides, you can override the render_graphql_ide method. 

from strawberry.fastapi import GraphQLRouter
from starlette.responses import HTMLResponse, Response
from starlette.requests import Request




class MyGraphQLRouter(GraphQLRouter):
    async def render_graphql_ide(self, request: Request) -> HTMLResponse:
        custom_html = """<html><body><h1>Custom GraphQL IDE</h1></body></html>"""


        return HTMLResponse(custom_html)

on_ws_connect

By overriding on_ws_connect you can customize the behavior when a graphql-ws or graphql-transport-ws connection is established. This is particularly useful for authentication and authorization. By default, all connections are accepted.

To manually accept a connection, return strawberry.UNSET or a connection acknowledgment payload. The acknowledgment payload will be sent to the client.

Note that the legacy protocol does not support None /null acknowledgment payloads, while the new protocol does. Our implementation will treat None /null payloads the same as strawberry.UNSET in the context of the legacy protocol.

To reject a connection, raise a ConnectionRejectionError . You can optionally provide a custom error payload that will be sent to the client when the legacy GraphQL over WebSocket protocol is used. 

from typing import Dict
from strawberry.exceptions import ConnectionRejectionError
from strawberry.fastapi import GraphQLRouter




class MyGraphQLRouter(GraphQLRouter):
    async def on_ws_connect(self, context: Dict[str, object]):
        connection_params = context["connection_params"]


        if not isinstance(connection_params, dict):
            # Reject without a custom graphql-ws error payload
            raise ConnectionRejectionError()


        if connection_params.get("password") != "secret":
            # Reject with a custom graphql-ws error payload
            raise ConnectionRejectionError({"reason": "Invalid password"})


        if username := connection_params.get("username"):
            # Accept with a custom acknowledgment payload
            return {"message": f"Hello, {username}!"}


        # Accept without a acknowledgment payload
        return await super().on_ws_connect(context)