Mocking resolvers in GraphQL - Mini Project: Build & Apply

Mocking Resolvers in GraphQL

📖 Scenario: You are building a simple GraphQL API for a bookstore. Before connecting to a real database, you want to create mock resolvers to simulate data fetching. This helps frontend developers start working without waiting for the backend to be fully ready.

🎯 Goal: Create a GraphQL schema for books and authors, then write mock resolvers that return fixed sample data for queries.

📋 What You'll Learn

Define a GraphQL schema with types Book and Author

Create a query type with books and authors fields

Write mock resolver functions that return fixed arrays of books and authors

Connect the schema and resolvers to create a working mock GraphQL server

💡 Why This Matters

🌍 Real World

Mocking resolvers lets frontend developers work with a GraphQL API before the real database and backend logic are ready.

💼 Career

Understanding how to mock GraphQL resolvers is useful for rapid prototyping, testing, and collaboration between frontend and backend teams.

1

Define the GraphQL schema

Create a GraphQL schema string called typeDefs with these exact types: Book with fields id: ID!, title: String!, authorId: ID!; Author with fields id: ID!, name: String!; and a Query type with fields books: [Book!]! and authors: [Author!]!.

GraphQL

# Your code here

Need a hint?

Use the gql template literal to define your schema string.

2

Create mock data arrays

Create two constant arrays called books and authors. books should contain exactly two objects with keys id, title, and authorId with values '1', 'The Great Gatsby', '1' and '2', '1984', '2'. authors should contain exactly two objects with keys id and name with values '1', 'F. Scott Fitzgerald' and '2', 'George Orwell'.

GraphQL

const { gql } = require('apollo-server');

const typeDefs = gql`
  type Book {
    id: ID!
    title: String!
    authorId: ID!
  }

  type Author {
    id: ID!
    name: String!
  }

  type Query {
    books: [Book!]!
    authors: [Author!]!
  }
`;

# Your code here

Need a hint?

Use arrays of objects with exact keys and values as specified.

3

Write mock resolver functions

Create a constant object called resolvers with a Query field. Inside Query, add two functions: books and authors. Each function should return the corresponding array books or authors.

GraphQL

const { gql } = require('apollo-server');

const typeDefs = gql`
  type Book {
    id: ID!
    title: String!
    authorId: ID!
  }

  type Author {
    id: ID!
    name: String!
  }

  type Query {
    books: [Book!]!
    authors: [Author!]!
  }
`;

const books = [
  { id: '1', title: 'The Great Gatsby', authorId: '1' },
  { id: '2', title: '1984', authorId: '2' }
];

const authors = [
  { id: '1', name: 'F. Scott Fitzgerald' },
  { id: '2', name: 'George Orwell' }
];

# Define resolvers object with Query field and functions
# Your code here

Need a hint?

Use arrow functions inside the Query object to return the arrays.

4

Create the Apollo Server with mocks

Create a constant called server by instantiating ApolloServer with an object containing typeDefs and resolvers. Use const { ApolloServer } = require('apollo-server'); at the top. This completes the mock GraphQL server setup.

GraphQL

const { gql, ApolloServer } = require('apollo-server');

const typeDefs = gql`
  type Book {
    id: ID!
    title: String!
    authorId: ID!
  }

  type Author {
    id: ID!
    name: String!
  }

  type Query {
    books: [Book!]!
    authors: [Author!]!
  }
`;

const books = [
  { id: '1', title: 'The Great Gatsby', authorId: '1' },
  { id: '2', title: '1984', authorId: '2' }
];

const authors = [
  { id: '1', name: 'F. Scott Fitzgerald' },
  { id: '2', name: 'George Orwell' }
];

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

# Instantiate ApolloServer with typeDefs and resolvers
# Your code here

Need a hint?

Import ApolloServer and create a new instance with your schema and resolvers.