class-validator decorators in NestJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of @IsString() decorator in class-validator?

The @IsString() decorator checks if the value of a property is a string. It helps ensure the data type is correct before processing.

beginner

How does @IsNotEmpty() decorator help in validation?

The @IsNotEmpty() decorator ensures that a property is not empty. It rejects empty strings, null, or undefined values to guarantee required data is present.

beginner

What does @IsEmail() decorator validate?

The @IsEmail() decorator checks if the property contains a valid email address format. It helps catch invalid emails early.

intermediate

Explain the use of @MinLength(5) decorator.

The @MinLength(5) decorator ensures the string property has at least 5 characters. It helps enforce minimum length rules like passwords or usernames.

intermediate

What is the role of @ValidateNested() decorator?

The @ValidateNested() decorator validates nested objects inside a class. It tells class-validator to check the inner object's decorators too.

Which decorator checks if a property is a number?

A @IsBoolean()

B @IsString()

C @IsNumber()

D @IsEmail()

The @IsNumber() decorator validates that the property is a number.

What does @IsOptional() do in class-validator?

A Makes a property required

B Skips validation if the property is missing

C Checks if a property is a string

D Validates nested objects

The @IsOptional() decorator skips validation if the property is not present.

Which decorator would you use to ensure a string is not empty?

A @IsNotEmpty()

B @IsEmail()

C @MinLength(1)

D @IsString()

@IsNotEmpty() ensures the property is not empty, rejecting empty strings.

How do you validate that a property is an array?

A @IsArray()

B @IsObject()

C @IsString()

D @IsNumber()

@IsArray() checks if the property is an array.

What is the use of @ValidateNested()?

A Makes a property optional

B Checks if a property is a number

C Ensures a string is an email

D Validates nested objects inside a class

@ValidateNested() tells class-validator to validate nested object properties.

Describe how you would use class-validator decorators to ensure a user signup form has a valid email, a password with minimum length 8, and an optional nickname.

Think about which decorators check format, length, and optional fields.

Explain why @ValidateNested() is important when validating objects that contain other objects.

Consider how validation works on nested data structures.