15-Batching and Caching in GraphQL with Data Loader

Author: rwieruch

server/package-lock.json

@@ -9,7 +9,7 @@
     "test": "mocha --require @babel/register 'src/**/*.spec.js'"
   },
   "keywords": [],
-  "author": "",
+  "author": "Robin Wieruch <hello@rwieruch.com> (https://www.robinwieruch.de)",
   "license": "ISC",
   "devDependencies": {
     "@babel/core": "^7.1.2",
@@ -26,6 +26,7 @@
     "apollo-server-express": "^2.1.0",
     "bcrypt": "^3.0.2",
     "cors": "^2.8.4",
+    "dataloader": "^1.4.0",
     "dotenv": "^6.1.0",
     "express": "^4.16.4",
     "graphql": "^14.0.2",

server/package.json

@@ -2,6 +2,7 @@ import 'dotenv/config';
 import cors from 'cors';
 import http from 'http';
 import jwt from 'jsonwebtoken';
+import DataLoader from 'dataloader';
 import express from 'express';
 import {
   ApolloServer,
@@ -11,6 +12,7 @@ import {
 import schema from './schema';
 import resolvers from './resolvers';
 import models, { sequelize } from './models';
+import loaders from './loaders';
 
 const app = express();
 
@@ -49,6 +51,11 @@ const server = new ApolloServer({
     if (connection) {
       return {
         models,
+        loaders: {
+          user: new DataLoader(keys =>
+            loaders.user.batchUsers(keys, models),
+          ),
+        },
       };
     }
 
@@ -59,6 +66,11 @@ const server = new ApolloServer({
         models,
         me,
         secret: process.env.SECRET,
+        loaders: {
+          user: new DataLoader(keys =>
+            loaders.user.batchUsers(keys, models),
+          ),
+        },
       };
     }
   },

server/src/index.js

@@ -0,0 +1,3 @@
+import * as user from './user';
+
+export default { user };

server/src/loaders/index.js

@@ -0,0 +1,11 @@
+export const batchUsers = async (keys, models) => {
+  const users = await models.User.findAll({
+    where: {
+      id: {
+        $in: keys,
+      },
+    },
+  });
+
+  return keys.map(key => users.find(user => user.id === key));
+};

server/src/loaders/user.js

@@ -73,8 +73,8 @@ export default {
   },
 
   Message: {
-    user: async (message, args, { models }) => {
-      return await models.User.findById(message.userId);
+    user: async (message, args, { loaders }) => {
+      return await loaders.user.load(message.userId);
     },
   },