Resolvers in NestJS - Mini Project: Build & Apply

Building a Simple GraphQL Resolver in NestJS

📖 Scenario: You are creating a small NestJS GraphQL API for a bookstore. You want to provide a way for clients to get book details by their ID.

🎯 Goal: Build a GraphQL resolver in NestJS that returns a book object with id, title, and author fields when queried by id.

📋 What You'll Learn

Create a simple array of book objects with exact fields and values

Add a variable to hold the book ID to search for

Write a resolver method that returns the book matching the given ID

Complete the resolver class with the proper decorator and export

💡 Why This Matters

🌍 Real World

GraphQL resolvers in NestJS are used to handle client queries and return data from databases or other sources.

💼 Career

Understanding resolvers is essential for backend developers working with NestJS and GraphQL APIs.

1

Create the books data array

Create a constant array called books with these exact objects: { id: '1', title: '1984', author: 'George Orwell' }, { id: '2', title: 'Brave New World', author: 'Aldous Huxley' }, and { id: '3', title: 'Fahrenheit 451', author: 'Ray Bradbury' }.

NestJS

// Create the books array with 3 book objects
// Your code here

Need a hint?

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

2

Add the book ID variable

Create a constant called bookId and set it to the string '2' to represent the book to find.

NestJS

const books = [
  { id: '1', title: '1984', author: 'George Orwell' },
  { id: '2', title: 'Brave New World', author: 'Aldous Huxley' },
  { id: '3', title: 'Fahrenheit 451', author: 'Ray Bradbury' },
];

// Create a constant bookId with value '2'
// Your code here

Need a hint?

Use const bookId = '2'; exactly.

3

Write the resolver method to find the book

Create a method called getBookById that returns the book object from books where id matches bookId. Use find on the books array.

NestJS

const books = [
  { id: '1', title: '1984', author: 'George Orwell' },
  { id: '2', title: 'Brave New World', author: 'Aldous Huxley' },
  { id: '3', title: 'Fahrenheit 451', author: 'Ray Bradbury' },
];

const bookId = '2';

// Create a function getBookById that returns the book with id === bookId
// Your code here

Need a hint?

Use books.find(book => book.id === bookId) inside the function.

4

Complete the resolver class with decorator

Create a class called BookResolver decorated with @Resolver(). Inside it, add a method book decorated with @Query(() => Object) that calls and returns getBookById(). Export the class.

NestJS

const books = [
  { id: '1', title: '1984', author: 'George Orwell' },
  { id: '2', title: 'Brave New World', author: 'Aldous Huxley' },
  { id: '3', title: 'Fahrenheit 451', author: 'Ray Bradbury' },
];

const bookId = '2';

function getBookById() {
  return books.find(book => book.id === bookId);
}

// Create and export BookResolver class with @Resolver() decorator
// Add a @Query(() => Object) method named book that returns getBookById()
// Your code here

Need a hint?

Use @Resolver() on the class and @Query(() => Object) on the method.