Why DTOs enforce data contracts in NestJS - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a DTO class property with a type.

NestJS

export class CreateUserDto {
  username: [1];
}

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

Aany

Bnumber

Cboolean

Dstring

Attempts:

3 left

💡 Hint

Common Mistakes

Using number or boolean for username type.

Using any defeats the purpose of enforcing a data contract.

The username property should be a string to enforce the data contract for user names.

2fill in blank

medium

Complete the code to add validation decorator to a DTO property.

NestJS

import { IsString } from 'class-validator';

export class CreateUserDto {
  @[1]()
  username: string;
}

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

AIsString

BIsDate

CIsBoolean

DIsNumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using @IsNumber() or other decorators that don't match the property type.

Forgetting to add any validation decorator.

The @IsString() decorator ensures the username is validated as a string, enforcing the data contract.

3fill in blank

hard

Fix the error in the DTO by completing the missing decorator to enforce required property.

NestJS

import { IsString, [1] } from 'class-validator';

export class CreateUserDto {
  @IsString()
  @[1]()
  username: string;
}

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

AIsOptional

BIsEmail

CIsNotEmpty

DIsNumber

Attempts:

3 left

💡 Hint

Common Mistakes

Using @IsOptional() which allows the property to be missing.

Using unrelated decorators like @IsEmail() or @IsNumber().

The @IsNotEmpty() decorator ensures the username is not empty, enforcing the data contract that this field is required.

4fill in blank

hard

Fill both blanks to create a DTO property with type and validation decorator.

NestJS

import { [1] } from 'class-validator';

export class UpdateUserDto {
  @[2]()
  email: string;
}

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

AIsEmail

BIsString

CIsNotEmpty

DIsBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Importing or using @IsString() instead of @IsEmail().

Using unrelated decorators like @IsBoolean().

The email property should be validated with @IsEmail() decorator and import to enforce the email format as part of the data contract.

5fill in blank

hard

Fill both blanks to define a DTO with multiple validated properties.

NestJS

import { [1], [2] } from 'class-validator';

export class RegisterUserDto {
  @[1]()
  username: string;

  @[2]()
  age: number;
}

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

AIsString

BIsInt

CIsNotEmpty

DIsBoolean

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up decorators and imports.

Using IsNotEmpty or IsBoolean incorrectly.

The username is validated as a string with @IsString(), and age is validated as an integer with @IsInt(). Both decorators are imported accordingly to enforce the data contract.