Resolver chains in GraphQL - Mini Project: Build & Apply

Building a Resolver Chain in GraphQL

📖 Scenario: You are creating a simple GraphQL API for a bookstore. The API needs to fetch book details and then fetch the author details for each book using resolver chains.

🎯 Goal: Build a GraphQL resolver chain where the book resolver fetches book data and the author resolver fetches author data based on the book's author ID.

📋 What You'll Learn

Create a books array with exact book entries

Create an authors array with exact author entries

Write a Query resolver for book that returns a book by id

Write a Book type resolver for author that returns the author details for the book

💡 Why This Matters

🌍 Real World

GraphQL APIs often need to fetch related data from different sources. Resolver chains let you fetch nested data cleanly and efficiently.

💼 Career

Understanding resolver chains is essential for backend developers working with GraphQL to build scalable and maintainable APIs.

1

DATA SETUP: Create the books array

Create a constant array called books with these exact objects: { id: '1', title: '1984', authorId: 'a1' } and { id: '2', title: 'Brave New World', authorId: 'a2' }.

GraphQL

// Your code here

Need a hint?

Use const books = [ ... ] with exact objects inside.

2

CONFIGURATION: Create the authors array

Create a constant array called authors with these exact objects: { id: 'a1', name: 'George Orwell' } and { id: 'a2', name: 'Aldous Huxley' }.

GraphQL

const books = [
  { id: '1', title: '1984', authorId: 'a1' },
  { id: '2', title: 'Brave New World', authorId: 'a2' }
];
// Your code here

Need a hint?

Use const authors = [ ... ] with exact objects inside.

3

CORE LOGIC: Write the Query resolver for book

Write a Query resolver object with a book function that takes parent, args, and returns the book from books where book.id === args.id.

GraphQL

const books = [
  { id: '1', title: '1984', authorId: 'a1' },
  { id: '2', title: 'Brave New World', authorId: 'a2' }
];

const authors = [
  { id: 'a1', name: 'George Orwell' },
  { id: 'a2', name: 'Aldous Huxley' }
];

const resolvers = {
  Query: {
    // Your code here
  }
};

Need a hint?

Use books.find(book => book.id === args.id) inside the book resolver.

4

COMPLETION: Write the Book type resolver for author

Add a Book resolver object inside resolvers with an author function that takes parent and returns the author from authors where author.id === parent.authorId.

GraphQL

const books = [
  { id: '1', title: '1984', authorId: 'a1' },
  { id: '2', title: 'Brave New World', authorId: 'a2' }
];

const authors = [
  { id: 'a1', name: 'George Orwell' },
  { id: 'a2', name: 'Aldous Huxley' }
];

const resolvers = {
  Query: {
    book(parent, args) {
      return books.find(book => book.id === args.id);
    }
  },
  // Your code here
};

Need a hint?

Inside resolvers, add Book with an author resolver that finds the author by parent.authorId.