using System;

using System.Collections.Generic;

using System.ComponentModel.DataAnnotations;

using System.Linq;

public class Program

{

    public static void Main()

    {

        Valid();

        InvalidMissingValue();

        AddressTooLong();

    }

    public static void InvalidMissingValue()

    {

        ReaderSetting readerSetting = new() { RfidAddress = "" };

        EntityValidator<ReaderSetting> validator = new EntityValidator<ReaderSetting>();

        var result = validator.Validate(readerSetting);     

        Console.WriteLine($"{nameof(InvalidMissingValue)} {(result.IsValid ? "Yes" : "No")}");      

        result.Errors.ToList().ForEach(x => Console.WriteLine(x.ErrorMessage));     

        Console.WriteLine("");

    }

    public static void AddressTooLong()

    {

        ReaderSetting readerSetting = new() { RfidAddress = "some value" };

        EntityValidator<ReaderSetting> validator = new EntityValidator<ReaderSetting>();

        var result = validator.Validate(readerSetting);     

        Console.WriteLine($"{nameof(AddressTooLong)} {(result.IsValid ? "Yes" : "No")}");

        result.Errors.ToList().ForEach(x => Console.WriteLine(x.ErrorMessage));     

        Console.WriteLine("");      

    }

    public static void Valid()

    {

        ReaderSetting readerSetting = new() { RfidAddress = "abc" };

        EntityValidator<ReaderSetting> validator = new EntityValidator<ReaderSetting>();

        var result = validator.Validate(readerSetting);     

        Console.WriteLine($"{nameof(Valid)} {(result.IsValid ? "Yes" : "No")}");        

        result.Errors.ToList().ForEach(x => Console.WriteLine(x.ErrorMessage));     

        Console.WriteLine("");      

    }   

}

    public class ReaderSetting

    {

        //[JsonPropertyName("RfidAddress")]

        [Required(AllowEmptyStrings = false, ErrorMessage = "RFID Address is required.")]

        [StringLength(3, ErrorMessage = "Max Length is 3")]

        public string RfidAddress { get; set; }

    }

​

    public class EntityValidationResult

    {

        public IList<ValidationResult> Errors { get; set; }

        public bool IsValid => Errors.Count == 0;

        public EntityValidationResult(IList<ValidationResult> errors = null)

        {

            Errors = errors ?? new List<ValidationResult>();

        }

    }

    public class EntityValidator<T> where T : class

    {

        public EntityValidationResult Validate(T entity)

        {

            var validationResults = new List<ValidationResult>();

            var vc = new ValidationContext(entity, null, null);

            Validator.TryValidateObject(entity, vc, validationResults, true);

​

            return new EntityValidationResult(validationResults);

        }

    }