Route handlers (GET, POST, PUT, DELETE) in NestJS - Mini Project: Build & Apply

Basic CRUD API with NestJS Route Handlers

📖 Scenario: You are building a simple API for managing a list of books in a library. Each book has a title and an author.This API will let users get the list of books, add a new book, update an existing book, and delete a book.

🎯 Goal: Create a NestJS controller with route handlers for GET, POST, PUT, and DELETE to manage books.

📋 What You'll Learn

Create a controller class named BooksController.

Create a property books initialized with an array of two book objects: { id: 1, title: '1984', author: 'George Orwell' } and { id: 2, title: 'The Hobbit', author: 'J.R.R. Tolkien' }.

Add a GET route handler method getAllBooks() that returns the books array.

Add a POST route handler method addBook() that accepts a book object and adds it to books.

Add a PUT route handler method updateBook() that accepts an id parameter and a book object, then updates the matching book in books.

Add a DELETE route handler method deleteBook() that accepts an id parameter and removes the matching book from books.

💡 Why This Matters

🌍 Real World

APIs like this are common in web applications to manage data resources such as books, users, or products.

💼 Career

Understanding how to create route handlers for different HTTP methods is essential for backend development roles using NestJS or similar frameworks.

1

Create the initial books data array

Create a controller class named BooksController with a property books initialized to an array containing exactly these two objects: { id: 1, title: '1984', author: 'George Orwell' } and { id: 2, title: 'The Hobbit', author: 'J.R.R. Tolkien' }.

NestJS

export class BooksController {
  // Your code here
}

Hint

Define a class named BooksController. Inside it, create a property books and assign the array with the two book objects.

2

Add a GET route handler to return all books

Add a method named getAllBooks() decorated with @Get() that returns the books array.

NestJS

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

  // Add a GET route handler method getAllBooks() below
}

Hint

Use the @Get() decorator above the getAllBooks() method. Return the books property inside the method.

3

Add POST and PUT route handlers to add and update books

Add a POST route handler method addBook() decorated with @Post() that accepts a book object parameter decorated with @Body() and adds it to books. Also add a PUT route handler method updateBook() decorated with @Put(':id') that accepts an id parameter decorated with @Param('id') and a book object decorated with @Body(), then updates the matching book in books.

NestJS

import { Controller, Get, Post, Put, Body, Param } from '@nestjs/common';

@Controller('books')
export class BooksController {
  books = [
    { id: 1, title: '1984', author: 'George Orwell' },
    { id: 2, title: 'The Hobbit', author: 'J.R.R. Tolkien' }
  ];

  @Get()
  getAllBooks() {
    return this.books;
  }

  // Add POST and PUT route handlers addBook() and updateBook() below
}

Hint

Use @Post() and @Put(':id') decorators. Use @Body() to get the book data and @Param('id') to get the id. Update the books array accordingly.

4

Add DELETE route handler to remove a book

Add a DELETE route handler method deleteBook() decorated with @Delete(':id') that accepts an id parameter decorated with @Param('id') and removes the matching book from books.

NestJS

import { Controller, Get, Post, Put, Delete, Body, Param } from '@nestjs/common';

@Controller('books')
export class BooksController {
  books = [
    { id: 1, title: '1984', author: 'George Orwell' },
    { id: 2, title: 'The Hobbit', author: 'J.R.R. Tolkien' }
  ];

  @Get()
  getAllBooks() {
    return this.books;
  }

  @Post()
  addBook(@Body() book: { id: number; title: string; author: string }) {
    this.books.push(book);
  }

  @Put(':id')
  updateBook(
    @Param('id') id: string,
    @Body() updatedBook: { title: string; author: string }
  ) {
    const bookId = Number(id);
    const bookIndex = this.books.findIndex(book => book.id === bookId);
    if (bookIndex !== -1) {
      this.books[bookIndex] = { id: bookId, ...updatedBook };
    }
  }

  // Add DELETE route handler deleteBook() below
}

Hint

Use the @Delete(':id') decorator. Use @Param('id') to get the id. Use filter to remove the book from the array.

Practice

1. Which decorator is used in NestJS to create a route handler that responds to HTTP GET requests?

easy

A. @Get

B. @Post

C. @Put

D. @Delete

Solution

1. Step 1: Understand HTTP methods and their decorators

   In NestJS, each HTTP method has a specific decorator: @Get for GET, @Post for POST, @Put for PUT, and @Delete for DELETE.

2. Step 2: Match the decorator to the GET method

   The decorator @Get is specifically designed to handle HTTP GET requests.

3. Final Answer:

   @Get -> Option A

4. Quick Check:

   GET method uses @Get decorator [OK]

Hint: GET requests use @Get decorator in NestJS [OK]

Common Mistakes:

• Confusing @Post or @Put with @Get
• Using @Delete for GET requests
• Not using any decorator

2. Which of the following is the correct syntax to define a POST route handler in a NestJS controller?

easy

A. @Post('/create') createItem() {}

B. Post('/create') createItem() {}

C. @post('/create') createItem() {}

D. @Put('/create') createItem() {}

Solution

1. Step 1: Check the decorator syntax

   Decorators in NestJS start with '@' and are case-sensitive. The correct decorator for POST is '@Post'.

2. Step 2: Verify the route path and method name

   The route path '/create' is correctly passed as a string argument, and the method name is valid.

3. Final Answer:

   @Post('/create') createItem() {} -> Option A

4. Quick Check:

   Correct decorator syntax uses '@Post' with parentheses [OK]

Hint: Decorators start with '@' and are case-sensitive [OK]

Common Mistakes:

• Missing '@' before decorator
• Using lowercase '@post' instead of '@Post'
• Using wrong decorator like '@Put' for POST

3. Given the following NestJS controller code, what will be the HTTP method and route path to access the handler?

@Controller('users')
export class UserController {
  @Put(':id')
  updateUser() {
    return 'User updated';
  }
}

medium

A. GET /users/:id

B. DELETE /users/:id

C. PUT /users/:id

D. POST /users/:id

Solution

1. Step 1: Identify the controller base path

   The @Controller('users') decorator sets the base route path to '/users'.

2. Step 2: Identify the route handler method and path

   The @Put(':id') decorator means this handler responds to HTTP PUT requests at the path '/users/:id', where ':id' is a route parameter.

3. Final Answer:

   PUT /users/:id -> Option C

4. Quick Check:

   @Put with ':id' means PUT method at /users/:id [OK]

Hint: Decorator @Put means HTTP PUT method [OK]

Common Mistakes:

• Confusing @Put with @Get or @Post
• Ignoring the controller base path
• Misreading ':id' as a literal string

4. What is wrong with this NestJS route handler code?

@Controller('items')
export class ItemController {
  @Delete('/remove')
  removeItem() {
    console.log('Item removed');
  }
}

medium

A. The method name must be 'deleteItem' for @Delete decorator

B. The decorator @Delete cannot have a path argument

C. The controller path 'items' is invalid

D. The method should return a value, not just console.log

Solution

1. Step 1: Check the decorator and path usage

   @Delete can have a path argument like '/remove', so this is valid.

2. Step 2: Check the method implementation

   The method only logs to console but does not return any response. HTTP handlers should return a response to the client.

3. Final Answer:

   The method should return a value, not just console.log -> Option D

4. Quick Check:

   Route handlers must return a response [OK]

Hint: Route handlers must return a response, not just log [OK]

Common Mistakes:

• Assuming console.log sends response
• Thinking decorator cannot have path
• Believing method name must match decorator

5. You want to create a NestJS controller with a route handler that updates a product by its ID using HTTP PUT. The handler should accept the ID as a route parameter and the updated data in the request body. Which code snippet correctly implements this?

hard

A. @Put updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; }

B. @Put(':id') updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; }

C. @Put(':id') updateProduct(id: string, data: any) { return `Updated product ${id}`; }

D. @Post(':id') updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; }

Solution

1. Step 1: Use the correct HTTP method and route parameter

   Updating a resource uses HTTP PUT, so @Put(':id') is correct to capture the ID as a route parameter.

2. Step 2: Use parameter decorators to access route and body data

   @Param('id') extracts the ID from the route, and @Body() extracts the request body data. Both are required for this handler.

3. Step 3: Check method signature and return

   The method correctly returns a string confirming the update with the ID.

4. Final Answer:

   @Put(':id') updateProduct(@Param('id') id: string, @Body() data: any) { return `Updated product ${id}`; } -> Option B

5. Quick Check:

   Use @Put with ':id' and @Param plus @Body [OK]

Hint: Use @Put(':id') with @Param and @Body for updates [OK]

Common Mistakes:

• Missing route parameter in @Put decorator
• Not using @Param or @Body decorators
• Using wrong HTTP method like @Post for update