I can't succeed to correctly handle exceptions in NestJs - rest

Question

I'm trying to learn NestJs by creating a CRUD API.
I've created my controller, module, service etc...
And created a get users/id endpoint. Everything worked fine, and I decided to add some security.
I want to check if the id is not null and is a string. If not, I want to throw an exception (bad request) + console.log a message.
I also want to check if when I look for a user with a good if, the user exists. if not, throw a not found exception.
Here is my service:
async findOne(id: string): Promise<IUser | null> {
if (id === null || typeof id !== 'string') {
throw new BadRequestException('Id must be a string');
}
const user = await this.userModel.findById(id).exec();
if (user === null) {
throw new NotFoundException('No user found for this id');
}
return user;
}
and controller:
#Get(':id')
async find(#Param('id') id: string) {
try {
return await this.userService.findOne(id);
} catch (error) {
if (error instanceof BadRequestException) {
throw new HttpException(
{
status: HttpStatus.FORBIDDEN,
error: 'This is a custom message',
},
HttpStatus.FORBIDDEN,
{
cause: error,
},
);
} else if (error instanceof NotFoundException) {
throw new HttpException(
{
status: HttpStatus.NOT_FOUND,
error: 'This is a custom not found message',
},
HttpStatus.NOT_FOUND,
{
cause: error,
},
);
}
}
}
The problem is when I try a get request with .../users/1111 ,I got a 200 response. And when I try with a good id (a string) but with no user linked, I also get a 200 response.
I don't understand why.. Can you help me please ?
I also want to log the message.
And have you any advices ? Is the right way (standard + elegant) to do ?
Thanks guys ;)

Answer 1

In your code you are checking id to be of a type string and not null. Technically any param is a string, so even 1111 becomes "1111". You can verify that by logging it like so console.log({ id }) (expected result: { id: "1111" }).
For the validation I would suggest to follow the documentation on validation pipes: NestJS documentation.
TLDR;
The following code will add a global pipe to validate payloads
app.module.ts (copied from NestJS | Pipes)
import { Module } from '#nestjs/common';
import { APP_PIPE } from '#nestjs/core';
#Module({
providers: [
{
provide: APP_PIPE,
useClass: ValidationPipe,
},
],
})
export class AppModule {}
To make it work you will need to have class-validator and class-transformer installed, so run:
npm i --save class-validator class-transformer
Then declare a class that will serve as a blueprint of a DTO (Data Transfer Object), like so:
import { IsString, IsNotEmpty } from 'class-validator';
export class IdDto {
#IsNotEmpty()
#IsString()
id: string;
}
Then in your controller use the IdDto:
#Get(':id')
async find(#Param() { id }: IdDto) {
...
This already should be enough to have a basic validation. Moreover, this will convert the payload to a format that you expect (or fail and throw validation error). It is done via plainToClass method exposed from class-transformer. So there won't be any surprises with JavaScript type coercion like "1" + 1 = "11".
If you need to format your exceptions (or enrich them with additional data) you can use exception filters. There is a nice documentation about it in the official documentation.
Hope that helps!