sunildy / graphql-chain

GraphQL middleware similar to Express's middleware

GraphQL Chain

Create GraphQL middleware that resembles how Express middleware works.

Install

yarn add graphql-chain

How to use

Step 1

Create middleware

const validationMiddleware: MiddlewareResolver = (
  next,
  parent,
  args,
  context,
  info
) => {
  if (args.name.length > 10) {
    throw new Error("too long");
  }

  return next();
};

It has access to all the regular parameters a resolver gets plus a next parameter at the beginning which you call and return to call the next middleware or resolver.

You don't always have to call the next middleware or resolver though. This can be helpful if you want create a caching middleware:

const cachingMiddleware: MiddlewareResolver = async (next, _, args) => {
  const data = await redis.get("hello:cache");
  if (data) {
    // found data in the cache, so return early
    console.log("CACHE HIT");
    return data;
  }
  // did not find data, so call the next middleware
  console.log("CACHE MISS");
  const result = await next();
  // set cache for next call
  await redis.set("hello:cache", result);
  return result;
};

You can also change the value of the arguments and then use them later

const getUserMiddleware: MiddlewareResolver = async (next, _, __, context) => {
  if (validToken(context.authToken)) {
    // you can add properties to context that you can use later
    context.user = await getUser(context.authToken);
  }

  return next();
};

So you can then have a middleware that checks the user

const authorizationMiddleware: MiddlewareResolver = (next, _, __, context) => {
  if (!context.user || !context.user.admin) {
    throw new Error("not authorized");
  }

  return next();
};

Step 2

Chain as many middlewares together as you like

import { chain } from "graphql-chain";

const helloMiddleware = chain([
  getUserMiddleware,
  authorizationMiddleware,
  validationMiddleware
]);

Step 3

Wrap the resolver you want the middleware to run on

const resolvers: IResolvers = {
  Query: {
    hello: helloMiddleware((_, { name }) => `Hello ${name || "World"}`)
  }
};

The execution sequence will be getUserMiddleware -> authorizationMiddleware -> validationMiddleware -> hello

Checkout the examples directory for complete examples