While reviewing the official nestjs documentation, I encountered an interesting implementation of ValidationPipe:
import { PipeTransform, Injectable, ArgumentMetadata, BadRequestException } from '@nestjs/common';
import { validate } from 'class-validator';
import { plainToClass } from 'class-transformer';
@Injectable()
export class ValidationPipe implements PipeTransform<any> {
async transform(value: any, { metatype }: ArgumentMetadata) {
if (!metatype || !this.toValidate(metatype)) {
return value;
}
const object = plainToClass(metatype, value);
const errors = await validate(object);
if (errors.length > 0) {
throw new BadRequestException('Validation failed');
}
return value;
}
private toValidate(metatype: Function): boolean {
const types: Function[] = [String, Boolean, Number, Array, Object];
return !types.includes(metatype);
}
}
I am struggling to comprehend the algorithm utilized in the transform method. It would be extremely helpful if someone could elaborate on this code line by line. My confusion arises from a lack of understanding about what ArgumentMetadata represents and its origin.