Validation does not work when I use Validator.TryValidateObject - asp.net-mvc

Question

DataAnnotations does not work with buddy class. The following code always validate true. Why ?
var isValid = Validator.TryValidateObject(new Customer(), Context, results, true);
and here is the buddy class.
public partial class Customer
{
public string Name { get; set; }
public int Age { get; set; }
}
[MetadataType(typeof(CustomerMetaData))]
public partial class Customer
{
public class CustomerMetaData
{
[Required(ErrorMessage = "You must supply a name for a customer.")]
public string Name { get; set; }
}
}
Here is another thread with same question., but no answer.
link text

Answer 1

I found the answer here: http://forums.silverlight.net/forums/p/149264/377212.aspx
MVC recognizes the MetaDataType attribute, but other projects do not. Before validating, you need to manually register the metadata class:
TypeDescriptor.AddProviderTransparent(
new AssociatedMetadataTypeTypeDescriptionProvider(typeof(Customer), typeof(CustomerMetadata)), typeof(Customer));
var isValid = Validator.TryValidateObject(new Customer(), context, results, true);

Answer 2

After some research I couldn't find any reason why TryValidateObject always return true if I use MetadataType (buddy class). But it works with the following code (xVal).
public static IEnumerable<ErrorInfo> GetErrors(object instance, string name)
{
var metadataAttrib = instance.GetType()
.GetCustomAttributes(typeof(MetadataTypeAttribute), true)
.OfType<MetadataTypeAttribute>().FirstOrDefault();
var buddyClassOrModelClass = metadataAttrib != null
? metadataAttrib.MetadataClassType
: instance.GetType();
var buddyClassProperties = TypeDescriptor.GetProperties(buddyClassOrModelClass)
.Cast<PropertyDescriptor>();
var modelClassProperties = TypeDescriptor.GetProperties(instance.GetType())
.Cast<PropertyDescriptor>();
var list = from buddyProp in buddyClassProperties
join modelProp in modelClassProperties on
buddyProp.Name equals modelProp.Name
from attribute in buddyProp.Attributes.OfType<ValidationAttribute>()
where !attribute.IsValid(modelProp.GetValue(instance))
select new ErrorInfo(
buddyProp.Name,
attribute.FormatErrorMessage(modelProp.Name),
instance);
if (name != null)
list = list.Where(x => x.PropertyName == name);
return list;
}

Answer 3

Although I did not test your code in .NET 4.0, in .NET 3.5 / Silverlight 3, your metadata class should look like this:
[MetadataType(typeof(Customer.CustomerMetaData))]
public partial class Customer
{
internal sealed class CustomerMetaData
{
private CustomerMetaData()
{
}
[Required(ErrorMessage = "You must supply a name for a customer.")]
public string Name;
}
}

Answer 4

There is an issue where the MetadataType attribute is not being recognized by the object context. While you can manually add the type descriptor before validation:
TypeDescriptor.AddProviderTransparent(
new AssociatedMetadataTypeTypeDescriptionProvider(typeof(Customer), typeof(CustomerMetaData)), typeof(Customer));
a more concise way to handle it would be to update the Entity Model .tt file, to add the following to each DTO:
Type currentType = MethodBase.GetCurrentMethod().DeclaringType;
object[] attributes = currentType.GetCustomAttributes(typeof(MetadataTypeAttribute),false);
if(attributes.Length > 0)
{
//MetadataType attribute found!
MetadataTypeAttribute metaDataAttribute = (MetadataTypeAttribute)attributes[0];
TypeDescriptor.AddProviderTransparent(
new AssociatedMetadataTypeTypeDescriptionProvider(
currentType, metaDataAttribute.MetadataClassType),currentType);
}
This will allow you to add the attributes to the partial classes:
[MetadataType(typeof(CustomerMetaData))]
public partial class Customer
{
}
public partial class CustomerMetaData
{
[Required]
public string CustomerName { get; set; }
}