Question

I am trying to model a sort of “multiple inheritence” relationship with EF 4.1 Code First. Here is an example what I am trying to do.

Let’s say I am attempting to model the way a user interacts with my application using a “User” object. This, being the base class, is used to describe the current user when they aren’t doing anything in particular (such as visiting the homepage). It may look like this:

public class User
{
    public Guid ID { get; set; }    // Just use the forms authentication user ID
    public string FirstName { get; set; }
    public string LastName { get; set; }
}

Now, if I want to create a representation of that same user but in a different portion of the site, say, as a shopper, it may look like this:

public class Shopper : User
{
    public virtual ICollection<Orders> Orders { get; set; }
}

And so on, and so forth. When I go to insert a Shopper that has a pre-existing User entry, it throws an exception because the PK is already taken in the User table.

Is there any way to model this (IsA) relationship with EF Code First? Or am I going to be stuck with something like this?

public class Shopper
{
    public Guid UserID { get; set; }
    public virtual User User { get; set; }
    public virtual ICollection<Order> Orders { get; set; }

    public string FirstName
    {
        get { return User.FirstName; }
        set { User.FirstName = value; }
    }

    // yada, yada, yada...
}

I would like to stick with Code First and model the relationships right in my DbContext, but I can’t figure out quite how to do something like this. Thanks!

EDIT:

So, I am trying to do something like this:

public void SomeMethod ()
{
    var UserID = Guid.NewGuid ();
    var MyUser = new User () { ID = UserID };
    SaveUserToDatabase (MyUser);

    var ShopperRepresentation = GetUserAsShopper (UserID);
    //  Do stuff.
}

Basically like using object-oriented roles, I guess. I want to use the same PK for every represenation of that user, but store all of their basic information in a base class called User. I know this is possible if I write my own SQL, of course, but I want to see if EF Code First can do it, too.

Answer 1

Yes, you can do it the way you describe in your first two code examples.

I think you just need to define a mapping, which you’ll want to do in your OnModelCreating function of your DataContext in addition to having your classes set up right. How you do it depends on what mapping scheme you’re using. I went for Table-Per-Type (TPT) in my most recent project, so I had something like this:

modelBuilder.Entity<User>().ToTable("Users");
modelBuilder.Entity<Shopper>().ToTable("Shoppers");
modelBuilder.Entity<OtherUser>().ToTable("OtherUsers");

Let me know if that doesn’t work for you and I’ll see what I can do.

Edit:

Having seen your clarification below, I can’t think of a way to do that. You’d have to keep each objects stored separately (having EF treat a Shopper as just a Shopper, not a Shopper and a User), even though they share common data. That could lead to data mismatches (if, say, Shopper got its LastName updated but User didn’t). I think you might be better off going with something like:

public class User
{
    public virtual Guid ID { get; set; }
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual ShopperInfo { get; set; }
}

public class ShopperInfo
{
    public virtual ICollection<Order> Orders { get; set; }
}

and then when you need to treat User as a Shopper, you just access the ShopperInfo (and if its not there, you create it). EF will be able to properly set that up for you no problem.

Though if you’re going to have a lot of types of users, that might get cumbersome. Just a suggestion though – I think its a bit cleaner.