Repository pattern in NestJS - Mini Project: Build & Apply

Repository Pattern in NestJS

📖 Scenario: You are building a simple NestJS service to manage a list of books in a library. You want to organize your code using the Repository pattern to separate data access logic from business logic.

🎯 Goal: Create a basic repository class to store and retrieve books, then use it in a service class to fetch all books.

📋 What You'll Learn

Create a Book interface with id and title properties

Create a BookRepository class with a private array of books

Add a method findAll() in BookRepository to return all books

Create a BookService class that uses BookRepository to get all books

💡 Why This Matters

🌍 Real World

The Repository pattern helps organize code in backend applications like NestJS by separating data access from business logic. This makes code easier to maintain and test.

💼 Career

Understanding the Repository pattern is important for backend developers working with NestJS or similar frameworks to build clean, scalable applications.

1

Define the Book interface and initial data

Create an interface called Book with properties id (number) and title (string). Then create a constant array called books with two books: one with id: 1 and title: 'NestJS Basics', and another with id: 2 and title: 'Advanced NestJS'.

NestJS

// Define the Book interface and the books array
// Your code here

Need a hint?

Use interface to define the shape of a book object. Then create an array with two book objects exactly as described.

2

Create the BookRepository class with books array

Create a class called BookRepository. Inside it, add a private property called books and assign it the books array you created earlier.

NestJS

interface Book {
  id: number;
  title: string;
}

const books: Book[] = [
  { id: 1, title: 'NestJS Basics' },
  { id: 2, title: 'Advanced NestJS' }
];

// Create BookRepository class with private books property
// Your code here

Need a hint?

Define a class and add a private property named exactly books that holds the array of books.

3

Add findAll() method to BookRepository

Inside the BookRepository class, add a method called findAll() that returns the books array.

NestJS

interface Book {
  id: number;
  title: string;
}

const books: Book[] = [
  { id: 1, title: 'NestJS Basics' },
  { id: 2, title: 'Advanced NestJS' }
];

class BookRepository {
  private books = books;

  // Your code here
}

Need a hint?

Write a method named findAll that returns the private books property.

4

Create BookService using BookRepository

Create a class called BookService. Add a private property called bookRepository and initialize it with a new instance of BookRepository. Then add a method called getAllBooks() that calls findAll() on bookRepository and returns the result.

NestJS

interface Book {
  id: number;
  title: string;
}

const books: Book[] = [
  { id: 1, title: 'NestJS Basics' },
  { id: 2, title: 'Advanced NestJS' }
];

class BookRepository {
  private books = books;

  findAll(): Book[] {
    return this.books;
  }
}

// Create BookService class using BookRepository
// Your code here

Need a hint?

Create a service class that holds an instance of BookRepository and uses it to get all books.