asp.NET MVC 3 Composite pattern model binding - asp.net-mvc-3

Question

My application has products and vendors and both of them have similar items in a "has a" relationship...in particular they have a "favorite" so users can bookmark them.
so we have:
public class Product
{
public int ProductId {get;set;}
public int Name {get;set;}
public List<Favorite> Favorites {get;set;}
}
public class Vendor
{
public int VendorId {get;set;}
public int Name {get;set;}
public List<Favorite> Favorites {get;set;}
}
public class Favorite
{
public int FavoriteId {get;set;}
public string UserName {get;set;}
}
At first this didn't work, so I added:
public int? VendorId {get;set;}
public int? ProductId {get;set;}
Now the issue I'm having is that my Vendor.Favorites and Product.Favorites are always null.
How do I bind these so that I can work with the objects like that? Do I not make it a separate entity?
Thanks!
UPDATE: I should note that I'm using MVC 3 Code-first with POCO.
UPDATE: Solution:
I don't think this is ideal, still working out the kinks with how I want this to work because It will add redundant code for adding favorites and reviews.
public class Product
{
public int ProductId {get;set;}
public int Name {get;set;}
public virtual List<Favorite> Favorites {get;set;}
}
public class Vendor
{
public int VendorId {get;set;}
public int Name {get;set;}
public virtual List<Favorite> Favorites {get;set;}
}
Having the raw nullable int variable in the favorites class makes it work, but if I wanted to use the favorites class with other objects I'll have to modify the favorites properties with a new mapping to the key of the object. Out of curiosity, when dealing with these classes normally, how do you manage the data storage for these objects? I'm assuming you deal with it at a DAL?

Answer 1

You could use inheritance, make a base class containing only Favorite then derive classes based on that for the other info. This establishes an "is a" relationship
Ex.
public class baseClass
{
public list<Favorite> Favorites { get; set;}
}
public class Product : base
{
public int ProductID { get; set; }
public string Name { get; set; }
}
Then a Product Object would have all 3 properties.

Answer 2

Based on the assumption that you're using EF 4.1:
Your model looks pretty good except I'd change
public int? VendorId {get;set;}
public int? ProductId {get;set;}
to
public virtual Vendor VendorId {get;set;}
public virtual Product ProductId {get;set;}
Then your FK relationships should be all set. By my understanding of EF, List<Favorite> is meant to establish a relationship and is not actually populated. You have to populate it yourself, either by calling .Include() on the context or by referencing the actual FK that EF creates in the database, which in your case would be VendorId_FavoriteId or ProductId_FavoriteId

Answer 3

I would keep one Property to store the ID's (either VendorID or ProductId) and use another property to tell me what type it is (Vendor or Product)
public class Favorite
{
public int FavoriteId {get;set;}
public string UserName {get;set;}
public int ItemID { set;get;} //can use a better generic name
public FavoriteType Type { set;get;}
}
I have an Enum for the Types
public enum FavoriteType
{
Vendor,
Product
}
And make sure you are initializing your sub properties before accessing them / applying a method on those so that It won't throw the null reference exception!. You can do it constructor itself
public class Product
{
public int ProductId {get;set;}
public int Name {get;set;}
public List<Favorite> Favorites {get;set;}
public Product()
{
if(Favourites==null)
Favorites=new List<Favorite>();
}
}