Never Show The Same Thing Twice!

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@dismissible/nestjs-validation

A validation service for NestJS applications using class-validator and class-transformer.

> Part of the Dismissible API - This library is part of the Dismissible API ecosystem. Visit dismissible.io for more information and documentation.

Overview

This library provides a ValidationService that wraps class-validator and class-transformer to provide a consistent validation API for DTOs and class instances in NestJS applications.

Installation

``bash
npm install @dismissible/nestjs-validation
`

You'll also need to install the peer dependencies:

`bash
npm install class-validator class-transformer
`

Getting Started

$3

`typescript
import { Module } from '@nestjs/common';
import { ValidationModule } from '@dismissible/nestjs-validation';

@Module({
imports: [ValidationModule],
})
export class AppModule {}
`

$3

The ValidationService can validate plain objects against DTO classes:

`typescript
import { Injectable } from '@nestjs/common';
import { ValidationService } from '@dismissible/nestjs-validation';
import { IsString, IsEmail, IsOptional } from 'class-validator';

class CreateUserDto {
@IsString()
name!: string;

@IsEmail()
email!: string;

@IsOptional()
@IsString()
phone?: string;
}

@Injectable()
export class UserService {
constructor(private readonly validationService: ValidationService) {}

async createUser(data: unknown) {
// Validates and transforms the data, throws BadRequestException if invalid
const dto = await this.validationService.validateDto(CreateUserDto, data);

// dto is now a validated instance of CreateUserDto
// Use dto.name, dto.email, etc.
}
}
`

$3

You can also validate class instances that have already been created:

`typescript
import { Injectable } from '@nestjs/common';
import { ValidationService } from '@dismissible/nestjs-validation';
import { IsString, IsDate } from 'class-validator';

class MyDto {
@IsString()
name!: string;

@IsDate()
createdAt!: Date;
}

@Injectable()
export class MyService {
constructor(private readonly validationService: ValidationService) {}

async validateInstance(dto: MyDto) {
// Validates the instance, throws BadRequestException if invalid
await this.validationService.validateInstance(dto);
}
}
`

$3

The validation service throws BadRequestException with formatted error messages when validation fails:

`typescript
import { BadRequestException } from '@nestjs/common';
import { ValidationService } from '@dismissible/nestjs-validation';

@Injectable()
export class MyService {
constructor(private readonly validationService: ValidationService) {}

async handleRequest(data: unknown) {
try {
const dto = await this.validationService.validateDto(MyDto, data);
// Process valid data
} catch (error) {
if (error instanceof BadRequestException) {
// Handle validation errors
console.error('Validation failed:', error.message);
}
throw error;
}
}
}
`

API Reference

$3

#### validateDto(dtoClass, data): Promise

Validates and transforms plain data into a DTO instance.

Parameters:

- dtoClass: ClassConstructor - The DTO class to validate against
- data: unknown - The data to validate

Returns: Promise - A validated instance of the DTO class

Throws: BadRequestException if validation fails

#### validateInstance(instance): Promise

Validates an existing class instance.

Parameters:

- instance: T - The instance to validate

Throws: BadRequestException if validation fails

$3

A NestJS module that provides ValidationService as a singleton.

Exports:

- ValidationService - The validation service

Features

- Automatic transformation using class-transformer
- Validation using class-validator decorators
- Nested validation error extraction
- Formatted error messages
- Type-safe DTOs with TypeScript generics

Example: Using in a Controller

`typescript
import { Controller, Post, Body } from '@nestjs/common';
import { ValidationService } from '@dismissible/nestjs-validation';
import { IsString, IsEmail } from 'class-validator';

class CreateUserDto {
@IsString()
name!: string;

@IsEmail()
email!: string;
}

@Controller('users')
export class UserController {
constructor(private readonly validationService: ValidationService) {}

@Post()
async create(@Body() body: unknown) {
const dto = await this.validationService.validateDto(CreateUserDto, body);
// Use validated dto
return { message: Creating user: ${dto.name} };
}
}
`

Related Packages

This validation service is used by:

- @dismissible/nestjs-core` - Validates dismissible items

License

MIT