Add dataloaders to graphql context

graphqlExpress.js

import DataLoader from 'dataloader'
import {graphqlExpress} from 'graphql-server-express'
import schema from './schema'
import db from './database'

const contextFromReq = req => {
	const {session} = req

	const loaders = {}
	const getLoader = (id, makeGetter) => {
		const loader = loaders[id]
		if (loader) return loader
		const l = new DataLoader(makeGetter(db))
		loaders[id] = l
		return l
	}
	return {
		db,
		session,
		getLoader,
	}
}

export default graphqlExpress(req => {
	const context = contextFromReq(req)
	// http://dev.apollodata.com/tools/graphql-server/setup.html#graphqlOptions
	return {context, schema}
})

schemaPartWithLoader.js

const makeIdGetter = db => ids => db.fooTable.getAll(ids)

const query = {
	foo: {
		type: Foo,
		args: {
			id: {type: GraphQLID},
		},
		resolve: (root, {id}, {getLoader}) => getLoader('houseId', makeIdGetter).load(id),
  },
}