How to add unique field validation in nest js with class-validator

How to do validation with database like unique filed validation in nest JS using the class validator?

I created a custom validation class and tried it. But userService was undefined when I console log that service in the validate function.

import { ValidatorConstraint, ValidatorConstraintInterface, ValidationArguments } from 'class-validator';
import { Injectable } from '@nestjs/common';
import { UserService } from './user.service';

@ValidatorConstraint({ name: 'unique', async: true })
@Injectable()
export class UniqueFieldValidator implements ValidatorConstraintInterface {
  constructor(private readonly userService: UserService) {
  }

  validate = async (value: any, args: ValidationArguments): Promise<boolean> => {
    console.log(this.userService); // <-- This log prints undefined
    const [entityClass, fieldName] = args.constraints;
    const entity = await this.userService.findByFieldValue({ [fieldName]: value });
    return !entity;
  }

  defaultMessage(args: ValidationArguments) {
    const [entityClass, fieldName] = args.constraints;
    return `${fieldName} must be unique`;
  }
}

I have called this class in side createUserDto Class as below.

import { IsEnum, IsNotEmpty, MinLength, Validate } from "class-validator";
import { CompanyStatuses } from "src/company/dto/company.enums";
import { User } from "../entities/user.entity";
import { UniqueFieldValidator } from "../unique-field-validator";

export class CreateUserDto {

    @IsNotEmpty()
    @MinLength(3)
    @Validate(UniqueFieldValidator, [User, 'username'])
    username: string
}

UniqueFieldValidator class is calling successfully.
But because that userServices is undefined in the validate function when I sent the request to create a user, it's returning the error message saying

    TypeError: Cannot read properties of undefined (reading 'findByFieldValue')
    at UniqueFieldValidator.validate

If anyone has experience this in NestJs with class-validator please help me. Thank you!

P.S.

Below code shows how i have written my userModule and i have added both UserService and Validator class to the Providers array.also have placed @injectable() decorator top of the UserService class. but it's not working still.

import { Module } from '@nestjs/common';
import { UserService } from './user.service';
import { UserController } from './user.controller';
import { TypeOrmModule } from '@nestjs/typeorm';
import { User } from './entities/user.entity';
import { UniqueFieldValidator } from './unique-field-validator';

@Module({
  controllers: [UserController],
  providers: [UserService,UniqueFieldValidator],
  imports: [TypeOrmModule.forFeature([User])],
  exports: [UserService,TypeOrmModule]
})
export class UserModule { }

Yeah! I found a solution and posting it to my own question for help to someone getting this issue in the future.
Just add useContainer(app.select(AppModule), { fallbackOnErrors: true }); in your root method.

Then my main.ts was like this.

import { NestFactory } from '@nestjs/core';
import { AppModule } from './app.module';
import { useContainer } from 'class-validator';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);
  useContainer(app.select(AppModule), { fallbackOnErrors: true });
  await app.listen(3000);
}
bootstrap();

I'm posting this to my own question to help someone in the future.