Data Annotations Validator

IViewModelValidator.cs

	public interface IViewModelValidator
	{
		bool IsValid(object model);
	}

	public class DataAnnotationsValidator : IViewModelValidator
	{
		private class ReferenceEqualityComparer : IEqualityComparer<object>
		{
			public new bool Equals(object x, object y)
			{
				return ReferenceEquals(x, y);
			}

			public int GetHashCode(object obj)
			{
				return RuntimeHelpers.GetHashCode(obj);
			}
		}

		public bool TryValidate(object model, out ICollection<ValidationResult> results)
		{
			var vrs = new List<ValidationResult>();
			results = vrs;
			return TryValidate(model, new HashSet<object>(new ReferenceEqualityComparer()), vrs);
		}

		public bool IsValid(object model)
		{
			return TryValidate(model, new HashSet<object>(new ReferenceEqualityComparer()), null);
		}

		private bool TryValidate(object model, ISet<object> validatedObjects, List<ValidationResult> results)
		{
			if (validatedObjects.Contains(model))
			{
				return true;
			}
			validatedObjects.Add(model);
			var shortcircuit = results == null;
			var context = new ValidationContext(model, serviceProvider: null, items: null);
			bool result = Validator.TryValidateObject(model, context, results, validateAllProperties: true);

			var properties = TypeDescriptor.GetProperties(model).Cast<PropertyDescriptor>().ToList();
			foreach (var property in properties.Where(p => p.PropertyType != typeof(string) && !p.PropertyType.IsValueType))
			{
				var value = property.GetValue(model);
				if (value == null)
				{
					continue;
				}
				if (value is IEnumerable asEnumerable)
				{
					foreach (var enumObj in asEnumerable)
					{
						if (enumObj != null)
						{
							var nestedResults = shortcircuit ? null : new List<ValidationResult>();
							if (!TryValidate(enumObj, validatedObjects, nestedResults))
							{
								if (shortcircuit)
								{
									return false;
								}
								result = false;
								results.AddRange(nestedResults.Select(nr => new ValidationResult(nr.ErrorMessage, nr.MemberNames.Select(x => property.Name + '.' + x))));
							};
						}
					}
				}
				else
				{
					var nestedResults = new List<ValidationResult>();
					if (!TryValidate(value, validatedObjects, nestedResults))
					{
						if (shortcircuit)
						{
							return false;
						}
						result = false;
						results.AddRange(nestedResults.Select(nr => new ValidationResult(nr.ErrorMessage, nr.MemberNames.Select(x => property.Name + '.' + x))));
					};
				}
			}
			return result;
		}
	}