Nest JS class-validators complex examples to make life easier in project

Hello I am working in JavaScript related technologies from last 5+ years, currently working as Full stack engineer in Cardekho, Product based company in India.

From last 2 years, I started working In NestJS which is a typescript based framework. I developed 3 microservices using NestJs in a single project —

1. Http Api Microservice
2. Cron Microservice
3. Consumer Microservice

On every micro service, We need to write class validators to validate input parameters, API Request Body & Query Params.

IN some cases class-validators are very typical and no documentation found , if you want to perform some complex validation, let me share some of great examples may made your life easier

Validate Array Of Mobile numbers

Input [“abc”, “8789”], error: “each value in mobile_numbers must match ^[5–9][0–9]{9}$ regular expression”

Validate Array Of objects

Input has buttons array with an Object

Example class validator example

Lets go more deeper in class validators —

1. Validating String

Any String

// example.dto.ts
import {
  IsString,
  IsNotEmpty,
  MinLength,
  MaxLength
} from 'class-validator'

export class AnyString {
    @IsString()
    @IsNotEmpty()
    @MinLength(3)
  @MaxLength(65)
    userName: string
}

Specific String

// example.dto.tsty
import {
  ArrayNotEmpty,
  IsArray,
    IsIn
} from 'class-validator'

const weekdays = ['monday', 'tuesday', 'wednesday', 'thursday', 'friday'];
export class SpecificString {
  @IsArray()
  @ArrayNotEmpty()
    @IsIn(weekdays)
  day: string[]
}

Array of strings

// example.dto.ts
import {
  ArrayNotEmpty,
  Contains,
  IsArray,
  IsString,
  Matches,
  MaxLength
} from 'class-validator'

export class StringArray {
  @IsArray()
  @ArrayNotEmpty()
  // check if every array item is string
  @IsString({ each: true }) 
    // Pass `each: true` when you want this validation to run on every array item
  // Check if every array item has max length
  @MaxLength(6, { each: true })
  // Check if every array item is only alphabets
  @Matches('^[a-zA-Z\\s]+$', undefined, { each: true })
  // CHeck if every array item contains a text
  @Contains('hello', { each: true })
  stringArray: string[]
}

Array of Strings with a custom prefix

// example.dto.ts
import {
  ArrayNotEmpty,
  IsArray,
  Validate,
  ValidateNested,
  ValidatorConstraint,
  ValidatorConstraintInterface
} from 'class-validator'

@ValidatorConstraint({ name: 'arrayPrefixValidator' })
export class ArrayPrefixValidator implements ValidatorConstraintInterface {
  validate(values: string[] = []): boolean {
    if (values.length) {
      return values.every((value) => value.startsWith('str-'))
    }
    return false
  }
}
export class StringArray {
  @IsArray()
  @ArrayNotEmpty()
  // Check if every array item contains a prefix str-
  @Validate(ArrayPrefixValidator, { message: 'No str- prefix' })
  stringArray: string[]
}

2️. Validating Number

Any number

import {
  IsNumber,
  IsNotEmpty,
  MinLength,
  MaxLength
} from 'class-validator'
export class AnyString {
    @IsNumber()
    @IsNotEmpty()
    @MinLength(3)
  @MaxLength(65)
    userName: string
}

Specific Number

import {
  IsNumber,
  IsNotEmpty,
  MinLength,
  MaxLength,
  ValidatorConstraint,
  ValidatorConstraintInterface
} from 'class-validator'
@ValidatorConstraint({ name: 'isDividedBy17' })
export class IsDividedBy17 implements ValidatorConstraintInterface {
  validate(value: number): boolean {
    if (value {
      return value % 17 === 0
    }
    return false
  }
}
export class SpecificNumber {
  @IsNumber()
    @IsNotEmpty()
  // Check if number is divisible by 17
  @Validate(IsDividedBy17, { message: 'No divided by 17' })
  specificNumber: number
}

Array of numbers

import {
  IsNumber,
  IsNotEmpty,
  MinLength,
  MaxLength,
  ValidatorConstraint,
  ValidatorConstraintInterface
} from 'class-validator'

@ValidatorConstraint({ name: 'isEvenNumber' })
export class IsEvenNumber implements ValidatorConstraintInterface {
  validate(numbers: number): boolean {
    if (numbers {
      return numbers.every(number => number % 2 === 0)
    }
    return false
  }
}
export class SpecificNumber {
  @IsNumber()
    @IsNotEmpty()
  // Check if everynumber is even
    @Validate(IsEvenNumber, { message: 'No divided by 17' })
  numbersList: number[]
}

3️. Custom Object

For example you have a payload like below

{
jsom    movies: [{
        name: "The jurassic park",
        yearOfRelease: 1999,
        languages: ["en"]
        gener: ["sci-fi", "thriller"]
    },
    {
        name: "The Croods",
        yearOfRelease: 2012,
        languages: ["en", "fr", "es"]
        gener: ["animation", "kids"]
    }]
}

import {
  IsNumber,
  IsNotEmpty,
  MinLength,
  MaxLength,
  ValidatorConstraint,
  ValidatorConstraintInterface
} from 'class-validator'

@ValidatorConstraint({ name: 'isEvenNumber' })
export class IsEvenNumber implements ValidatorConstraintInterface {
  validate(numbers: number): boolean {
    if (numbers {
      return numbers.every(number => number % 2 === 0)
    }
    return false
  }
}
const validLanguages = ["en", "es", "fr"] 
const validGeneres = ["sci-fi", "thriller", "animation", "horror", "vintage"]
// 💡 Types here
export class Movie {
  @IsString()
    @IsNotEmpty()
    @ISRequired()
  name: string
  @IsNotEmpty()
  @IsNumber()
    @ISRequired()
  yearOfRelease: number
  @IsNotEmpty()
  @IsString()
    @IsIn(validLanguages)
    @ISRequired()
  languages: string[]
  @IsNotEmpty()
  @IsString()
    @IsIn(validGeneres)
    @ISRequired()
  genre: string[]
}
export class MoviesList {
  @IsArray()
    @ArrayNotEmpty()
    @Type(() => Movie)
  movies: Movie[]
}

Please write in comment section if this was helpful in your use case, also u can write if need any help in your project.

References

Documentation | NestJS — A progressive Node.js framework

Top 5 class-validator Code Examples | Snyk