IsValid.ts

import { ArgumentMetadata, BadRequestException, Injectable, PipeTransform } from '@nestjs/common';
import { validate } from 'class-validator';
import { plainToClass } from 'class-transformer';

@Injectable()
export class IsValid implements PipeTransform<any> {
    async transform(value, metadata: ArgumentMetadata) {
        const { metatype } = metadata;
        if (!metatype || !this.toValidate(metatype)) {
            return value;
        }
        const object = plainToClass(metatype, value);
        const errors = await validate(object);
        if (errors.length > 0) {
            const constraints = errors[0].constraints;
            let message = 'Validation failed';
            for (const key in constraints) {
                if (constraints[key]) {
                    message = constraints[key];
                    break;
                }
            }
            throw new BadRequestException(message);
        }
        return value;
    }

    private toValidate(metatype): boolean {
        const types = [String, Boolean, Number, Array, Object];
        return !types.find(type => metatype === type);
    }
}