Controller decorator in NestJS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a basic controller with the correct decorator.

NestJS

import { [1] } from '@nestjs/common';

@[1]('cats')
export class CatsController {}

Drag options to blanks, or click blank then click option'

AInjectable

BService

CModule

DController

Attempts:

3 left

💡 Hint

Common Mistakes

Using @Injectable instead of @Controller

Forgetting to import the decorator

Using @Module or @Service which are not for controllers

The @Controller decorator defines a controller class in NestJS. It takes an optional route prefix like 'cats'.

2fill in blank

medium

Complete the code to create a controller with the route prefix 'dogs'.

NestJS

import { Controller } from '@nestjs/common';

@Controller('[1]')
export class DogsController {}

Drag options to blanks, or click blank then click option'

Adogs

Bcats

Cbirds

Dfish

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different route prefix than the controller name

Leaving the prefix empty when a specific route is needed

The string inside @Controller() sets the route prefix. Here, it should be 'dogs' to match the controller name.

3fill in blank

hard

Fix the error in the controller decorator import statement.

NestJS

import { [1] } from '@nestjs/common';

@Controller('users')
export class UsersController {}

Drag options to blanks, or click blank then click option'

AController

Bcontroller

CControllers

DControl

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'controller' instead of 'Controller'

Misspelling the decorator name

The decorator must be imported with exact casing: Controller. JavaScript and TypeScript are case-sensitive.

4fill in blank

hard

Fill both blanks to create a controller with route prefix 'products' and export it.

NestJS

[1] { Controller } from '@nestjs/common';

@[2]('products')
export class ProductsController {}

Drag options to blanks, or click blank then click option'

Aimport

Bexport

CInjectable

DController

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'export' instead of 'import' for bringing in decorators

Using 'Injectable' instead of 'Controller' as decorator

You must import the Controller decorator and then use @Controller('products') to define the route prefix.

5fill in blank

hard

Fill all three blanks to define and export a controller with route prefix 'orders'.

NestJS

[1] { [2] } from '@nestjs/common';

@[3]('orders')
export class OrdersController {}

Drag options to blanks, or click blank then click option'

Aexport

Bimport

CController

DInjectable

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'export' instead of 'import' for the first blank

Using 'Injectable' instead of 'Controller' for the decorator

You import the Controller decorator, then use @Controller('orders') to set the route prefix.

Practice

1. What is the main purpose of the @Controller decorator in NestJS?

easy

A. To define a service that handles business logic

B. To mark a class as a group of routes with a base path

C. To create a database connection

D. To style the HTML output of a component

Solution

1. Step 1: Understand the role of @Controller

   The @Controller decorator marks a class as a handler for HTTP requests grouped under a base path.

2. Step 2: Differentiate from other decorators

   It is not used for services, database, or styling but specifically for routing.

3. Final Answer:

   To mark a class as a group of routes with a base path -> Option B

4. Quick Check:

   @Controller = route group [OK]

Hint: Remember: @Controller groups routes under one path [OK]

Common Mistakes:

• Confusing @Controller with @Injectable
• Thinking it styles components
• Assuming it manages database connections

2. Which of the following is the correct syntax to define a controller with base path 'users' in NestJS?

easy

A. @Controller = 'users'
export class UsersController {}

B. @Controller.users
export class UsersController {}

C. @Controller('users')
export class UsersController {}

D. @Controller path='users'
export class UsersController {}

Solution

1. Step 1: Recall correct decorator syntax

   The @Controller decorator takes the base path as a string argument inside parentheses.

2. Step 2: Check each option's syntax

   Only @Controller('users') export class UsersController {} uses the correct syntax: @Controller('users'). Others misuse dot, equal sign, or invalid syntax.

3. Final Answer:

   @Controller('users') export class UsersController {} -> Option C

4. Quick Check:

   @Controller('path') syntax = @Controller('users') export class UsersController {} [OK]

Hint: Use parentheses with string path in @Controller [OK]

Common Mistakes:

• Using dot notation instead of parentheses
• Assigning with equal sign instead of decorator call
• Writing invalid decorator syntax

3. Given the following controller code, what is the full URL path to access the getAllUsers method?

@Controller('api')
export class UserController {
  @Get('users')
  getAllUsers() {
    return 'List of users';
  }
}

medium

A. /users

B. /users/api

C. /api/getAllUsers

D. /api/users

Solution

1. Step 1: Identify base path from @Controller

   The base path is 'api' from @Controller('api').

2. Step 2: Identify route path from @Get decorator

   The method route is 'users' from @Get('users').

3. Step 3: Combine base and method paths

   Full path is base + method = '/api/users'.

4. Final Answer:

   /api/users -> Option D

5. Quick Check:

   Base + method path = /api/users [OK]

Hint: Combine @Controller and @Get paths for full URL [OK]

Common Mistakes:

• Reversing base and method paths
• Using method name as URL path
• Ignoring base path in URL

4. Identify the error in this NestJS controller code:

@Controller('products')
export class ProductController {
  @Get()
  getAll() {
    return 'All products';
  }

  @Get('')
  getEmpty() {
    return 'Empty route';
  }
}

medium

A. Duplicate routes for the same path cause a conflict

B. Missing parentheses in @Get decorator

C. Controller path should be '/products' with a slash

D. Methods must return JSON objects, not strings

Solution

1. Step 1: Analyze route paths from @Get decorators

   Both methods respond to the same route: base 'products' + '' or no path means '/products'.

2. Step 2: Understand route conflict

   Having two methods for the same route causes a conflict and runtime error.

3. Final Answer:

   Duplicate routes for the same path cause a conflict -> Option A

4. Quick Check:

   Duplicate routes = conflict error [OK]

Hint: Avoid duplicate routes with same path in one controller [OK]

Common Mistakes:

• Focusing on @Get parentheses instead of duplicate routes
• Believing controller path needs leading slash
• Assuming string return type is invalid

5. You want to create a controller that handles routes for both '/admin' and '/user' paths using a single class. Which approach correctly uses the @Controller decorator to achieve this?

hard

A. Create two separate controllers, one for 'admin' and one for 'user'

B. @Controller(['admin', 'user'])
export class MultiPathController {}

C. @Controller('admin,user')
export class MultiPathController {}

D. @Controller('admin')
@Controller('user')
export class MultiPathController {}

Solution

1. Step 1: Understand @Controller supports single base path

   The @Controller decorator accepts a single string as the base path. It does not support multiple paths in an array.

2. Step 2: Evaluate options for multiple paths

   Create two separate controllers, one for 'admin' and one for 'user' is correct because creating two separate controllers is the proper way to handle multiple base paths. @Controller(['admin', 'user']) export class MultiPathController {} is invalid syntax. @Controller('admin,user') export class MultiPathController {} uses a comma-separated string which is treated as a single path. @Controller('admin') @Controller('user') export class MultiPathController {} uses multiple decorators which is invalid.

3. Final Answer:

   Create two separate controllers, one for 'admin' and one for 'user' -> Option A

4. Quick Check:

   One controller per base path [OK]

Hint: Use separate controllers for different base paths [OK]

Common Mistakes:

• Using array of strings in @Controller (not supported)
• Applying multiple @Controller decorators on one class
• Trying to combine multiple paths in one string