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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; } } }

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  • I'm not shure about this, but I think you shouldn't nest the classes. Also I think this could make CustomMetaData-class inaccessible without the public-keyword. Try moving CustomerMetaData out of the Customer-class and making it public. Commented Mar 11, 2010 at 1:56
  • It won't work even if I moving CustomerMetaData out of Customer class and declare as public. I have concern that does TryValidateObject support buddyclass (MetadataType)? Commented Mar 11, 2010 at 2:10

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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);
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Thanks. If I choose data annotation as my Validation framework then Validator.TryValidaeObject should validate from anywhere.
No constructor overload for AssociatedMetadataTypeTypeDescriptionProvider class takes three arguments. I see this issue with the code snippet.
The mistake I was making was in the use of TypeDescriptor.AddProviderTransparent call. AddProviderTransparent has two overloads. They differ in their second parameter. Initially I was trying to use the one with object parameter. It didn't work. When I replaced it with second overload having Type parameter then it worked. I wonder why first overload is not working: public static void AddProviderTransparent(TypeDescriptionProvider provider, object instance); public static void AddProviderTransparent(TypeDescriptionProvider provider, Type type);
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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; }
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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; } }
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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; } }
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Hello @Gareth Suarez, I think this is a great idea, can you provide more information on how to edit the Entity Model.tt file?
I actually tried to do it, but I don't know where should I include your snippet. I tried including it in the constructor of each DTO but I had no luck at all. Any idea? BTW, I'm trying to set the IgnoreDataMember in some of the attributes through MetadataType, this method should work, right?

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