Code-first approach in NestJS - Mini Project: Build & Apply

Building a GraphQL API with NestJS Code-First Approach

📖 Scenario: You are creating a simple GraphQL API for a bookstore. You want to define your data models and GraphQL schema using code, not schema files.

🎯 Goal: Build a NestJS GraphQL API using the code-first approach. You will create a book model, configure GraphQL, write a resolver to fetch books, and complete the module setup.

📋 What You'll Learn

Create a Book class with id, title, and author fields using GraphQL decorators

Add a configuration variable books as an array of book objects

Write a resolver method getBooks that returns the books array

Complete the AppModule to import GraphQLModule with code-first setup and register the resolver

💡 Why This Matters

🌍 Real World

Many modern APIs use GraphQL to allow clients to request exactly the data they need. NestJS's code-first approach lets developers define GraphQL schemas using familiar TypeScript classes and decorators.

💼 Career

Understanding how to build GraphQL APIs with NestJS is valuable for backend developers working on scalable and flexible APIs in Node.js environments.

1

Create the Book model with GraphQL decorators

Create a class called Book with fields id (number), title (string), and author (string). Use @ObjectType() on the class and @Field() on each field from @nestjs/graphql.

NestJS

import { ObjectType, Field, Int } from '@nestjs/graphql';

// Define the Book class with GraphQL decorators
// Your code here

Need a hint?

Use @ObjectType() above the class and @Field() above each property. For id, specify the type as Int.

2

Add a books array with sample data

Create a constant array called books with two book objects. Each object should have id, title, and author matching the Book class fields.

NestJS

import { ObjectType, Field, Int } from '@nestjs/graphql';

@ObjectType()
export class Book {
  @Field(type => Int)
  id: number;

  @Field()
  title: string;

  @Field()
  author: string;
}

// Create an array called books with two book objects
// Your code here

Need a hint?

Define books as an array of objects matching the Book structure.

3

Create a resolver with a query to get books

Create a class called BooksResolver. Use @Resolver(() => Book) on the class. Add a method getBooks decorated with @Query(() => [Book]) that returns the books array.

NestJS

import { ObjectType, Field, Int, Resolver, Query } from '@nestjs/graphql';

@ObjectType()
export class Book {
  @Field(type => Int)
  id: number;

  @Field()
  title: string;

  @Field()
  author: string;
}

export const books: Book[] = [
  { id: 1, title: '1984', author: 'George Orwell' },
  { id: 2, title: 'The Hobbit', author: 'J.R.R. Tolkien' },
];

// Define BooksResolver class with getBooks method
// Your code here

Need a hint?

Use @Resolver(() => Book) on the class and @Query(() => [Book]) on the method returning books.

4

Complete AppModule with GraphQLModule and resolver

In AppModule, import GraphQLModule from @nestjs/graphql and configure it with autoSchemaFile: true. Add BooksResolver to the providers array.

NestJS

import { ObjectType, Field, Int, Resolver, Query } from '@nestjs/graphql';
import { Module } from '@nestjs/common';
import { GraphQLModule } from '@nestjs/graphql';

@ObjectType()
export class Book {
  @Field(type => Int)
  id: number;

  @Field()
  title: string;

  @Field()
  author: string;
}

export const books: Book[] = [
  { id: 1, title: '1984', author: 'George Orwell' },
  { id: 2, title: 'The Hobbit', author: 'J.R.R. Tolkien' },
];

@Resolver(() => Book)
export class BooksResolver {
  @Query(() => [Book])
  getBooks(): Book[] {
    return books;
  }
}

@Module({
  // Add imports and providers here
  // Your code here
})
export class AppModule {}

Need a hint?

Use GraphQLModule.forRoot({ autoSchemaFile: true }) in imports and add BooksResolver to providers.