Nested resolver execution in GraphQL - Mini Project: Build & Apply

Nested Resolver Execution in GraphQL

📖 Scenario: You are building a simple GraphQL API for a bookstore. The API should return books along with their authors. Each book has a title and an author, and each author has a name and a list of books they wrote.

🎯 Goal: Create a GraphQL schema with nested resolvers so that when querying for books, you also get the author details, and when querying for authors, you get their books. This will demonstrate how nested resolver execution works in GraphQL.

📋 What You'll Learn

Create a Book type with fields title (String) and author (Author).

Create an Author type with fields name (String) and books (list of Book).

Create a root Query type with fields books and authors returning lists of Book and Author respectively.

Implement resolvers for books and authors queries.

Implement nested resolvers for author field in Book and books field in Author.

Use hardcoded data for books and authors to simulate a database.

💡 Why This Matters

🌍 Real World

GraphQL APIs often need to fetch related data in nested queries, such as fetching an author when querying a book. Understanding nested resolver execution helps build efficient and clear APIs.

💼 Career

Backend developers and API engineers use GraphQL nested resolvers to design flexible APIs that clients can query for exactly the data they need, improving performance and developer experience.

1

Define the GraphQL schema types

Create a GraphQL schema with Book and Author types. The Book type should have fields title (String) and author (Author). The Author type should have fields name (String) and books (list of Book).

GraphQL

type Book {
  title: String
  author: Author
}

type Author {
  name: String
  books: [Book]
}

# Define Book and Author types with the specified fields

Need a hint?

Define Book and Author types with the exact fields and types as described.

2

Add the root Query type with books and authors fields

Add a root Query type with two fields: books returning a list of Book, and authors returning a list of Author.

GraphQL

type Book {
  title: String
  author: Author
}

type Author {
  name: String
  books: [Book]
}

type Query {
  books: [Book]
  authors: [Author]
}

# Add Query type with books and authors fields

Need a hint?

Define the Query type with books and authors fields returning lists of the respective types.

3

Create hardcoded data and resolvers for books and authors

Create two arrays: books and authors with hardcoded data. Then create resolvers for the root Query fields books and authors that return these arrays.

GraphQL

const authors = [
  { id: 1, name: "Jane Austen" },
  { id: 2, name: "Mark Twain" }
];

const books = [
  { title: "Pride and Prejudice", authorId: 1 },
  { title: "Adventures of Huckleberry Finn", authorId: 2 }
];

const resolvers = {
  Query: {
    books: () => books,
    authors: () => authors
  }
};

# Create hardcoded data arrays and resolvers for Query fields

Need a hint?

Create arrays named books and authors with the exact data shown. Then create a resolvers object with a Query field that returns these arrays.

4

Add nested resolvers for author in Book and books in Author

Add nested resolvers inside resolvers for the Book type's author field and the Author type's books field. The author resolver should find the author by matching authorId in the book. The books resolver should find all books with authorId matching the author's id.

GraphQL

const authors = [
  { id: 1, name: "Jane Austen" },
  { id: 2, name: "Mark Twain" }
];

const books = [
  { title: "Pride and Prejudice", authorId: 1 },
  { title: "Adventures of Huckleberry Finn", authorId: 2 }
];

const resolvers = {
  Query: {
    books: () => books,
    authors: () => authors
  },
  Book: {
    author: (book) => authors.find(author => author.id === book.authorId)
  },
  Author: {
    books: (author) => books.filter(book => book.authorId === author.id)
  }
};

# Add nested resolvers for Book.author and Author.books

Need a hint?

Inside resolvers, add Book and Author objects with resolver functions for author and books fields respectively, using find and filter on the data arrays.