using System;

using System.ComponentModel.DataAnnotations;

using System.Reflection;

public class Program

{

    public static void Main()

    {

        var objectToValidate = new Foo() { Bar = "123456789012345678901121212" };

        var properties = objectToValidate.GetType().GetProperties();

        foreach (var property in properties)

        {

            var attributes = property.GetCustomAttributes<ValidationAttribute>();

            foreach (var attribute in attributes)

            {

                bool isValid = attribute.IsValid(property.GetValue(objectToValidate));

                if (!isValid)

                {

                    Console.WriteLine("{0} is invalid", property.Name); 

                }

            }

        }

    }

}

​

public class Foo

{

    [MaxLength(5)]

    public string Bar { get; set; } 

}