Why mutations modify data in GraphQL - See It in Action

Understanding Why Mutations Modify Data in GraphQL

📖 Scenario: You are building a simple GraphQL API for a small library. The library keeps track of books and their availability. You want to learn how to change data using GraphQL mutations.

🎯 Goal: Build a GraphQL mutation that modifies the availability status of a book in the library database.

📋 What You'll Learn

Create a GraphQL type Book with fields id, title, and available.

Create a mutation called updateBookAvailability that takes id and available as inputs.

The mutation should update the available status of the book with the given id.

Return the updated Book object from the mutation.

💡 Why This Matters

🌍 Real World

GraphQL mutations are used in real applications to change data on the server, such as updating user profiles, posting comments, or changing inventory status.

💼 Career

Understanding how mutations modify data is essential for backend developers working with GraphQL APIs to build interactive and dynamic applications.

1

Define the Book type

Create a GraphQL type called Book with fields id of type ID!, title of type String!, and available of type Boolean!.

GraphQL

# Define the Book type with id, title, and available fields
# Your code here

Need a hint?

Use the type keyword to define a new GraphQL type. Make sure to use exclamation marks ! to mark fields as required.

2

Add the updateBookAvailability mutation signature

Add a mutation called updateBookAvailability that takes two arguments: id of type ID! and available of type Boolean!. The mutation should return a Book type.

GraphQL

type Book {
  id: ID!
  title: String!
  available: Boolean!
}

# Add the mutation signature for updateBookAvailability
# Your code here

Need a hint?

Define a Mutation type and add the mutation with the correct argument types and return type.

3

Implement the resolver logic to modify data

Write a resolver function called updateBookAvailability that takes id and available as arguments, finds the book by id in the books array, updates its available field, and returns the updated book.

GraphQL

type Book {
  id: ID!
  title: String!
  available: Boolean!
}

type Mutation {
  updateBookAvailability(id: ID!, available: Boolean!): Book
}

const books = [
  { id: "1", title: "1984", available: true },
  { id: "2", title: "Brave New World", available: true }
];

// Write the updateBookAvailability resolver function
// Your code here

Need a hint?

Use Array.find() to locate the book by id. Then change its available property and return the updated book.

4

Complete the schema with Query and Mutation types

Add a Query type with a field books that returns a list of Book. Also, export the full schema including Query and Mutation types.

GraphQL

type Book {
  id: ID!
  title: String!
  available: Boolean!
}

type Mutation {
  updateBookAvailability(id: ID!, available: Boolean!): Book
}

type Query {
  # Add books field here
}

const books = [
  { id: "1", title: "1984", available: true },
  { id: "2", title: "Brave New World", available: true }
];

const resolvers = {
  Mutation: {
    updateBookAvailability: (_, { id, available }) => {
      const book = books.find(book => book.id === id);
      if (book) {
        book.available = available;
      }
      return book;
    }
  }
};

// Export schema and resolvers
// Your code here

Need a hint?

Define a Query type with a books field returning a list of Book. Export the schema and resolvers for use in your GraphQL server.