using System;

using System.ComponentModel.DataAnnotations;

using System.Collections.Generic;

​

namespace ConsoleApp1

{

    public class Program

    {

        public static void Main(string[] args) 

        {

            var user = new Stuent() { Name = "Hardik", CourseList = new List<Course>() {

                new Course { CourseId = 1, CourseName = "English" },

                new Course { CourseId = 2, CourseName = "Maths" },

                new Course { CourseId = 3, CourseName = "" } // assign CourseName to pass validation

            } };

            var user1 = new Course();

            var context = new ValidationContext(user, null, null);

            var results = new List<ValidationResult>();

            Validator.TryValidateObject(user, context, results, true);

            if (results.Count > 0)

            {

                foreach (var item in results)

                {

                    Console.WriteLine(item.ErrorMessage);

                }

            }

            else

            {

                Console.WriteLine("Success");

            }

        }

​

        public class Stuent

        {

            [Required]

            public string Name { get; set; }

​

            // Add custom validation attribute

            [Required, ValidateObject]

            public List<Course> CourseList { get; set; }

​

        }

        public class Course

        {

            public int CourseId { get; set; }

            [Required(AllowEmptyStrings = false)]

            public string CourseName { get; set; }

​

        }

    }

​

    // Custom validation attribute class

​

    public class ValidateObjectAttribute : ValidationAttribute

    {

        protected override ValidationResult IsValid(object value, ValidationContext validationContext)

        {

            var list = value as List<ConsoleApp1.Program.Course>;

​

            foreach (var item in list)

            {

                var results = new List<ValidationResult>();

                var context = new ValidationContext(item, null, null);

​

                Validator.TryValidateObject(item, context, results, true);

​

                if (results.Count != 0)

                {

                    var compositeResults = new CompositeValidationResult(String.Format("Validation for {0} failed!", validationContext.DisplayName));

                    results.ForEach(compositeResults.AddResult);

​

                    return compositeResults;

                }

​

            }

            return ValidationResult.Success;

        }

    }

​

    public class CompositeValidationResult : ValidationResult

    {

        private readonly List<ValidationResult> _results = new List<ValidationResult>();

​

        public IEnumerable<ValidationResult> Results

        {

            get

            {

                return _results;

            }

        }

​

        public CompositeValidationResult(string errorMessage) : base(errorMessage) { }

        public CompositeValidationResult(string errorMessage, IEnumerable<string> memberNames) : base(errorMessage, memberNames) { }

        protected CompositeValidationResult(ValidationResult validationResult) : base(validationResult) { }

​

        public void AddResult(ValidationResult validationResult)

        {

            _results.Add(validationResult);

        }

    }

}