Validate any entity framework model from any .NET program

RexaValidation.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Diagnostics;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Module2_Hamedan_MohammadRezaTayyebi.Components
{
    public class RexaValidation
    {

        [Serializable]
        public class RexaException : Exception
        {
            public RexaException() { }
            public RexaException(string message) : base(message) { }
        }

        public RexaValidation(object modelInstance)
        {
            var validationContext = new ValidationContext(modelInstance, null, null);
            var results = new List<ValidationResult>();

            if (Validator.TryValidateObject(modelInstance, validationContext, results, true))
            {
                // Its OK
            }
            else
            {
                string t = String.Empty;
                foreach (var item in results)
                {
                    t += "\r\n - " + item.ErrorMessage;
                }

                throw new RexaException(t);
            }
        }
    }
}