example to recreate Laravel exists validation in nestjs using class-validation

exists.validator.ts

import { ValidatorConstraint, ValidatorConstraintInterface, ValidationArguments } from 'class-validator';
import { Injectable } from '@nestjs/common';
import { Repository } from 'typeorm';

@ValidatorConstraint({ name: 'exists', async: true })
@Injectable()
export class ExistsValidator implements ValidatorConstraintInterface {
  constructor(private readonly repository: Repository<any>) {}

  async validate(value: any, args: ValidationArguments) {
    const [entityClass, condition] = args.constraints;
    const result = await this.repository.findOne(entityClass, { where: condition(value) });
    return !!result;
  }

  defaultMessage(args: ValidationArguments) {
    const [entityClass] = args.constraints;
    return `${entityClass.name} not found`;
  }
}

some-example.dto.ts

import { IsNotEmpty, Validate } from 'class-validator';
import { ExistsValidator } from './exists.validator';
import { User } from './user.entity';

export class CreateUserDto {
  @IsNotEmpty()
  name: string;

  @Validate(ExistsValidator, [User, (value) => ({ email: value })])
  email: string;
}

validation.module.ts

import { Module } from '@nestjs/common';
import { ExistsValidator } from './exists.validator';

@Module({
  providers: [ExistsValidator],
})
export class ValidationModule {} // remember to import in AppModule ;)