One-to-many relationships in GraphQL - Mini Project: Build & Apply

One-to-many relationships in GraphQL

📖 Scenario: You are building a simple GraphQL API for a library system. Each author can write many books, but each book has only one author.

🎯 Goal: Create a GraphQL schema that models the one-to-many relationship between authors and their books. You will define types for Author and Book, set up the fields to connect them, and write a query to fetch authors with their books.

📋 What You'll Learn

Define a GraphQL type Author with fields id (ID!), name (String!), and books (list of Book)

Define a GraphQL type Book with fields id (ID!), title (String!), and author (Author)

Create a query type with a field authors that returns a list of Author

Set up the one-to-many relationship so that each author can have many books, and each book belongs to one author

💡 Why This Matters

🌍 Real World

Modeling one-to-many relationships is common in APIs for libraries, stores, blogs, and many other systems where one entity relates to many others.

💼 Career

Understanding how to design GraphQL schemas with relationships is essential for backend developers building modern APIs.

1

Define the Author and Book types

Create a GraphQL type called Author with fields id of type ID! and name of type String!. Also create a GraphQL type called Book with fields id of type ID! and title of type String!.

GraphQL

# Define Author and Book types with id and name/title fields
# Your code here

Need a hint?

Start by defining the two types with their basic fields. Don't add relationships yet.

2

Add the one-to-many relationship fields

Add a field called books to the Author type that returns a list of Book (use [Book]). Add a field called author to the Book type that returns an Author.

GraphQL

type Author {
  id: ID!
  name: String!
  # Add books field here
}

type Book {
  id: ID!
  title: String!
  # Add author field here
}

Need a hint?

Use square brackets [] to indicate a list of books for the author.

3

Create the Query type with authors field

Define a Query type with a field called authors that returns a list of Author (use [Author]).

GraphQL

type Author {
  id: ID!
  name: String!
  books: [Book]
}

type Book {
  id: ID!
  title: String!
  author: Author
}

# Define Query type with authors field
# Your code here

Need a hint?

The Query type is the entry point for fetching data. Add the authors field that returns a list of Author.

4

Complete the schema with relationships

Ensure the full schema includes the Author, Book, and Query types with the one-to-many relationship fields books in Author and author in Book. The authors query should return a list of authors.

GraphQL

# Review and finalize the schema with all types and relationships
# Your code here

Need a hint?

Make sure all parts are included exactly as before to complete the schema.