using System;

using FluentValidation;

​

using System.Collections.Generic;

using System.Linq;

​

​

public class TokenUpdateRequestDto

{

     public IEnumerable<string> CstTokenUniqueReferences { get; set; }

}

​

​

public class TokenValidator : AbstractValidator<TokenUpdateRequestDto>

{

    public TokenValidator()

    {

        RuleFor(x  => x.CstTokenUniqueReferences)

            .Must(x => x != null && x.Count() == 1).WithMessage("It should have one and only like baby");

    }

}

​

public class Program

{

    public static void Main()

    {

        var fail1 = new TokenUpdateRequestDto();

        var pass1 = new TokenUpdateRequestDto()

        {

                CstTokenUniqueReferences = new List<string>() {"token1"}

        };

        var fail2 = new TokenUpdateRequestDto(){

                CstTokenUniqueReferences = new List<string>() {"token1", "token2"}

        };

​

        var validator = new TokenValidator();

​

        PrintValidationResult(validator.Validate(fail1),"fail1:");

        PrintValidationResult(validator.Validate(pass1),"pass1:");

        PrintValidationResult(validator.Validate(fail2),"pass2:");

    }

​

    public static void PrintValidationResult(FluentValidation.Results.ValidationResult result,string objectName)

    {

        Console.WriteLine(objectName);

        if (result.IsValid)

        {

            Console.WriteLine("✅ Validation successful");

        }

        else

        {

            foreach (var error in result.Errors)

            {

                Console.WriteLine("❌ " + error.ErrorMessage);

            }

        }

        Console.WriteLine();

    }

}

​