Pipes & Validation

Built-in pipes & class-validator

Use ValidationPipe with class-validator decorators to automatically validate DTOs.

// dto
import { IsString, IsEmail, IsNumber } from 'class-validator';

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

  @IsEmail()
  email: string;

  @IsNumber()
  age: number;
}

// main.ts
app.useGlobalPipes(new ValidationPipe());

Custom pipes

Implement PipeTransform to create a custom pipe for unique validation or transformation logic.

@Injectable()
export class ParseIntPipe implements PipeTransform<string, number> {
  transform(value: string): number {
    const num = parseInt(value, 10);
    if (isNaN(num)) throw new BadRequestException();
    return num;
  }
}

@Get(':id')
findOne(@Param('id', ParseIntPipe) id: number) { ... }

ParseIntPipe on a route param

Route params arrive as strings. ParseIntPipe converts to a number or throws 400.

• GET /users/7 gives id = 7 (a number).
• GET /users/abc returns 400 Bad Request automatically.

import { Controller, Get, Param, ParseIntPipe } from '@nestjs/common';

@Controller('users')
export class UsersController {
  @Get(':id')
  findOne(@Param('id', ParseIntPipe) id: number) {
    return { id, type: typeof id };
  }
}

Output:

{"id":7,"type":"number"}

Quick check

Quick check: `ValidationPipe` does not reject unknown properties by default. Which option strips them?

• `whitelist: true`
• `transform: false`
• `skipMissingProperties: true`