Email Verification with Class-Validator in nestJS

Yes, this is possible to validate email using class-validator

First of all you need to create custom class for this validator like this for example.

@ValidatorConstraint({ name: 'isEmailUserAlreadyExist', async: true })
    @Injectable()
    export class IsEmailUserAlreadyExistConstraint
      implements ValidatorConstraintInterface
    {
      constructor(protected readonly usersService: UsersService) {}
    
      async validate(text: string) {
        return !(await this.usersService.userExists({
          email: text,
        }));
      }
    }
    
    export function IsEmailUserAlreadyExist(validationOptions?: ValidationOptions) {
      return function (object: any, propertyName: string) {
        registerDecorator({
          target: object.constructor,
          propertyName: propertyName,
          options: validationOptions,
          constraints: [],
          validator: IsEmailUserAlreadyExistConstraint,
        });
      };
    }

Then you need to import this class to the users module

providers: [UsersService, IsEmailUserAlreadyExistConstraint]

And after all, you can use this custom decorator in you DTO, where you can pass custom message as the error output

  @IsEmailUserAlreadyExist({
    message: 'Пользователь с таким email уже существует',
  })
  readonly email: string;