GraphQL Next.js API route with `@graphql-tools` schema stitching

graphql.ts

import {isProduction} from '@/utils';
import {Executor} from '@graphql-tools/delegate';
import {makeExecutableSchema} from '@graphql-tools/schema';
import {stitchSchemas} from '@graphql-tools/stitch';
import {introspectSchema, wrapSchema} from '@graphql-tools/wrap';
import {graphqlHTTP} from 'express-graphql';
import {GraphQLSchema, print} from 'graphql';
import fetch from 'isomorphic-unfetch';
import {NextApiRequest, NextApiResponse} from 'next';
import getConfig from 'next/config';

const {serverRuntimeConfig} = getConfig();

export const config = {
  api: {
    bodyParser: false,
  },
};

const createLocalSchema = () =>
  makeExecutableSchema({
    resolvers: {
      Query: {
        hello: () => 'Hello from Next.js!',
      },
    },
    typeDefs: `
      type Query {
        hello: String!
      }
    `,
  });

const createDgraphSchema = async () => {
  const executor: Executor = async ({document, variables}) => {
    const query = print(document);
    const result = await fetch(serverRuntimeConfig.dgraphEndpoint, {
      method: 'POST',
      headers: {'Content-Type': 'application/json'},
      body: JSON.stringify({query, variables}),
    });
    return result.json();
  };
  return wrapSchema({
    executor,
    schema: await introspectSchema(executor as any),
  });
};

let schemaGateway: GraphQLSchema;

const getSchemaGateway = async () => {
  if (!schemaGateway) {
    schemaGateway = stitchSchemas({
      subschemas: [
        {schema: createLocalSchema()},
        {schema: await createDgraphSchema()},
      ],
    });
  }
  return schemaGateway;
};

const createHandler = async () =>
  graphqlHTTP({
    graphiql: !isProduction,
    schema: await getSchemaGateway(),
  });

export default async function graphql(
  req: NextApiRequest,
  res: NextApiResponse
) {
  return (await createHandler())(req as any, res);
}