Problems with ValidationPipe in NestJS when I need to validate the contents of an array - node.js

Question

I have a situation where my client user can enter zero or multiple addresses. My problem is that if he enters an address, some fields need to be mandatory.
user.controller.ts
#Post()
#UsePipes(ValidationPipe)
async createUser(
#Body() createUser: CreateUserDto,
) {
return await this.service.saveUserAndAddress(createUser);
}
create-user.dto.ts
export class CreateUserDto {
#IsNotEmpty({ message: 'ERROR_REQUIRED_FULL_NAME' })
fullName?: string;
#IsNotEmpty({ message: 'ERROR_REQUIRED_PASSWORD' })
password?: string;
#IsNotEmpty({ message: 'ERROR_REQUIRED_EMAIL' })
#IsEmail({}, { message: 'ERROR_INVALID_EMAIL' })
email?: string;
...
addresses?: CreateUserAddressDto[];
}
create-user-address.dto.ts
export class CreateUserAddressDto {
...
#IsNotEmpty()
street: string;
...
}
CreateUserDto data is validated correctly and generates InternalServerErrorResponse, but CreateUserAddressDto data is not validated when there is some item in my array. Any idea how I can do this validation?

Answer 1

Nest fw uses class-transformer to convert a json to a class object. You have to set the correct type for the sub-attribute if it is not a primitive value. And your attribute is an array, you have to config to tell class-validator that it is an array, and validate on each item.
Let's update CreateUserDto
import { Type } from 'class-transformer';
import { ..., ValidateNested } from 'class-validator';
export class CreateUserAddressDto {
...
#ValidateNested({ each: true })
#Type(() => CreateUserAddressDto)
addresses?: CreateUserAddressDto[];
...
}

Answer 2

What you are trying to do is - to basically add logic to primitive validators provided out of the box with nest - aka - defining a custom validator.
This can be done by using the two classes ValidatorConstraint and ValidatorConstraintInterface provided by the class validator.
In order to sort this, transform the incoming input / club whatever data you want to validate at once into an object - either using a pipe in nestjs or sent it as an object in the API call itself, then attach a validator on top of it.
To define a custom validator:
import { ValidatorConstraint, ValidatorConstraintInterface } from 'class-validator';
/**
* declare your custom validator here
*/
#ValidatorConstraint({ name: 'MyValidator', async: false })
export class MyValidator implements ValidatorConstraintInterface {
/** return true when tests pass **/
validate(incomingObject: myIncomingDataInterface) {
try {
// your logic regarding what all is required in the object
const output = someLogic(incomingObject);
return output;
} catch (e) {
return false;
}
}
defaultMessage() {
return 'Address update needs ... xyz';
}
}
Once you have defined this, keep this safe somewhere as per your project structure. Now you just need to call it whenever you want to put this validation.
In the data transfer object,
// import the validator
import { Validate } from 'class-validator';
import { MyValidator } from './../some/safe/place'
export class SomeDto{
#ApiProperty({...})
#Validate(MyValidator)
thisBecomesIncomingObjectInFunction: string;
}
As simple as that.