asp.net mvc related nullable entities

I'm having some problems with Model.IsValid. I am trying to create a model similar to this...

class Article {
  int Id {get; set;}
  string Title {get; set;}

  Category Category {get; set;}
}

class Category {
  int Id {get; set;}
  string Name {get; set;}

  IList<Articles> Articles {get; set;}
}

I would like that the Article Category can be null. How开发者_运维问答ever Model.IsValid is always false when the Category is null.

Any help appreciated.

Hmmm ... are you sure the Model.IsValid is false because of category being null? I am asking this since I don't see any 'required' data annotations in the Category property in your domain object. OR if it is indeed failing when binding on the Category then you might need to create a custom model binder which is where I think - more likely a guess - your error is happening.