Why DTOs are not throwing Validation error in nestjs? - dto

Question

I am using DTO in my code, and I am getting the response as expected but in code DTOs are not throwing error for example
export class CreateCatDto {
readonly name: string;
readonly age: number;
readonly breed: string;
}
In this name, age, the breed is a required field and each has their data type but while running on the postman when I am not passing all the required field or only one field into postman body I am not getting any errors like age is required if I have passed other two fields or I have given value of the parameter not according to data type like:- age : twenty five then also it should throw error but I am not getting.
So, This is class created for
import { ApiProperty } from '#nestjs/swagger';
export class Cat {
#ApiProperty({ example: 'Kitty', description: 'The name of the Cat' })
name: string;
#ApiProperty({ example: 1, description: 'The age of the Cat' })
age: number;
#ApiProperty({
example: 'Maine Coon',
description: 'The breed of the Cat',
})
breed: string;
}
This is controller in which I am importing class and Dto.
import { Body, Controller, Get, Param, Post } from '#nestjs/common';
import {
ApiBearerAuth,
ApiOperation,
ApiResponse,
ApiTags,
} from '#nestjs/swagger';
import { CatsService } from './cats.service';
import { Cat } from './classes/cat.class';
import { CreateCatDto } from './dto/create-cat.dto';
#ApiBearerAuth()
#ApiTags('cats')
#Controller('cats')
export class CatsController {
constructor(private readonly catsService: CatsService) {}
#Post()
#ApiOperation({ summary: 'Create cat' })
#ApiResponse({ status: 403, description: 'Forbidden.' })
async create(#Body() createCatDto: CreateCatDto): Promise<Cat> {
return this.catsService.create(createCatDto);
}
}

Answer 1

I don't know why you selected nestjs-swagger tag, DTO by itself will not validate inputs, maybe you need to use a ValidationPipe with the class-validator package as suggested on docs https://docs.nestjs.com/techniques/validation#validation
It's as simple as putting a decorator on your code now:
import { IsEmail, IsNotEmpty } from 'class-validator';
export class CreateCatDto {
#IsNotEmpty()
#IsString()
readonly name: string;
#IsNotEmpty()
#IsInt()
readonly age: number;
#IsNotEmpty()
readonly breed: string;
You can see all the items here: https://github.com/typestack/class-validator#validation-decorators
And if you want to sanitize the request body, you should use a serializer to help:
https://docs.nestjs.com/techniques/serialization#serialization
This will show or hide your DTO properties based on decorators of each field. You need to install class-transformer package.
import { Exclude } from 'class-transformer';
export class UserEntity {
id: number;
firstName: string;
lastName: string;
#Exclude()
password: string;
constructor(partial: Partial<UserEntity>) {
Object.assign(this, partial);
}
}
It's important to remember that interceptors will run on your request and response.