Validation

Validation is the process of ensuring that incoming data meets specific criteria before it is processed. In NestJS Validation is typically done using class-validator, which integrates well with DTOs to enforce rules like required fields, data types, length constraints

NestJS leverages Pipes to automatically validate incoming data based on the rules defined in DTOs.

First, install

pnpm add class-validator class-transformer

import { IsString, IsInt, Min, Max, IsNotEmpty } from 'class-validator';

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

  @IsInt()
  @Min(18)
  @Max(99)
  age: number;
}

Finally apply the validationpipe to a route handler

import { Body, Controller, Post, UsePipes, ValidationPipe } from '@nestjs/common';
import { CreateUserDto } from './create-user.dto';

@Controller('users')
export class UsersController {
  @Post()
  @UsePipes(new ValidationPipe())
  createUser(@Body() createUserDto: CreateUserDto) {
    // DTO will be validated automatically
    return this.usersService.create(createUserDto);
  }
}

DTO (Data Transfer Object)

A DTO is an object that defines how data will be sent over the network or between layers of an application. DTOs are usually used to encapsulated incoming request data and apply validation rules.

Why use DTOs?

• Separation of Concerns: separates business logic from the shape of incoming data
• Type Safety: DTOs provide type checking and validation
• Easy Validation: When combined with class-validator, DTOs provide a neat way to ensure that data meets specific criteria

export class CreateUserDto {
  readonly name: string;
  readonly age: number;
}

ORM (Object-Relational Mapping)

An ORM is a technique that allows you to interact with a relational database using object-oriented programming. ORMs map database tables to classes and rows to objects, abstracting away SQL queries and allowing you to use JavaScript/TypeScript to interact with the database.

TypeORM and Prisma are two commonly used ORMs

TypeORM

pnpm add @nestjs/typeorm typeorm pg