Home Courses GraphQL in 5 Days Day 4
Day 04 Real-Time

Subscriptions and Real-Time Data

WebSocket-based subscriptions, pub/sub patterns, and the cursor-based pagination that keeps GraphQL performant at scale.

~1 hour Intermediate Hands-on Precision AI Academy

Today's Objective

WebSocket-based subscriptions, pub/sub patterns, and the cursor-based pagination that keeps GraphQL performant at scale.

01

The Context Function

Context setup

import { ApolloServer } from '@apollo/server'; import { expressMiddleware } from '@apollo/server/express4'; import jwt from 'jsonwebtoken'; import User from './models/User.js'; const server = new ApolloServer({ typeDefs, resolvers }); await server.start(); app.use('/graphql', expressMiddleware(server, { context: async ({ req }) => { const token = req.headers.authorization?.split('Bearer ')[1]; let currentUser = null; if (token) { try { const { id } = jwt.verify(token, process.env.JWT_SECRET); currentUser = await User.findById(id); } catch {} } return { currentUser }; } }));

Using context in resolvers
const resolvers = {
  Query: {
    me: (_, __, { currentUser }) => {
      if (!currentUser) throw new Error('Not authenticated');
      return currentUser;
    },
  },
  Mutation: {
    createPost: (_, { input }, { currentUser }) => {
      if (!currentUser) throw new Error('Not authenticated');
      if (currentUser.role !== 'author') throw new Error('Not authorized');
      return createPost({ ...input, authorId: currentUser.id });
    }
  }
}
💡
Build a reusable requireAuth(context) helper function that throws if currentUser is null. Call it at the top of every protected resolver. Consistent error messages make debugging easier.
📝 Day 4 Exercise
Add Auth to Your GraphQL API
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Day 4 Summary

→
← Previous
Day 3: Mutations: Writing Data
Next →
Day 5: Apollo Client
→

What's Next

The foundations from today carry directly into Day 5. In the next session the focus shifts to Authentication, Authorization, and Federation — building directly on everything covered here.

Supporting Videos & Reading

Go deeper with these external references.

YouTube
Subscriptions and Real-Time Data — Video Walkthroughs Community tutorials and walkthroughs covering the concepts in this lesson.
→
YouTube
Subscriptions and Real-Time Data Explained Deep-dive explanations and live-coding sessions from top educators.
→
Official Docs
Official Documentation Primary reference documentation for the technologies covered in this lesson.
→
GitHub
Open Source Examples Real-world codebases demonstrating the patterns taught in this lesson.
→

Day 4 Checkpoint

Before moving on, verify you can answer these without looking:

  • What is the core concept introduced in this lesson, and why does it matter?
  • What are the two or three most common mistakes practitioners make with this topic?
  • Can you explain the key code pattern from this lesson to a colleague in plain language?
  • What would break first if you skipped the safeguards or best practices described here?
  • How does today's topic connect to what comes in Day 5?

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Continue To Day 5
Day 5: Apollo Client
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