Object validation attribute that tells the DataAnnotations validator that we want to validate a child object properties

ValidateObjectAttribute.cs

using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

namespace Utilities
{

    // Credit http://www.technofattie.com/2011/10/05/recursive-validation-using-dataannotations.html
    // Usage
    // 
    // class ParentObject {
    //    [ValidateObject]
    //    public SubObjecy { get; set;}
    //    ...
    // }

    public class ValidateObjectAttribute : ValidationAttribute
    {
        protected override ValidationResult IsValid(object value, ValidationContext validationContext)
        {
            var results = new List<ValidationResult>();
            var context = new ValidationContext(value, null, null);

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

            if (results.Count != 0)
            {
                var errorMsg = (string.IsNullOrEmpty(ErrorMessage)) ? String.Format("Validation for {0} failed!", validationContext.DisplayName) : ErrorMessage;
                var compositeResults = new CompositeValidationResult(errorMsg);
                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);
        }
    }
}