Question

Im using the above technologies and have ran into what I presume is a design issue I have made.

I have an Artwork table in my DB and have been able to add art (I now think of these as Digital Products) to a shopping cart + CartLine table fine. The system I have that adds art to galleries and user accounts etc works fine.

Now the client wants to sell T-shirts, Mugs and Pens etc, ‘HardwareProducts’ so I have created a ‘HardwareProducts’ table.

Now I have two different product types in two tables. I use GUID’s as the PK’s in both the HardwareProducts table and Artwork table. When a customer adds an item to their cart I store the GUID in the ProductID column in the CartItems table.

The issue is the database will not know which table to reference when I bring the LineItem object up through my ORM to the front end.

In OOP I can see how you would have a base class of Product, and then a DigitalProduct class and HardwareProduct class drived from it, but how do you model this in SQL Server and the Entity Framework please, or is there another way?

EDIT:

This is what I have in a test app at the moment thanks to the below comments. The trick that did it for me was utilising the ORM simular to what Stephane pointed out. It lead me to this excellent article.

alt text http://img411.imageshack.us/img411/3568/32654541.jpg

Allows:

int prodCount = _entities.Product.OfType<ArtWork>().Count();
IEnumerable<LineItem> lineItem = _entities.LineItem.Include("Product");
int artWorkCount = lineItem.Select(p => p.Product).OfType<ArtWork>().Count();

ArtWork prod = new ArtWork();
            prod.Price = 2;
            prod.ProductName = "atlast";
            prod.Downloads = 3;
            prod.GalleryID = 1;
            _entities.AddToProduct(prod);
            _entities.SaveChanges();

I am about to integrate it into my main solution and will let you know if I have anymore findings, but I think all is looking good. NB It appears the Type column which was mentioned, was not actually needed in the end which was a nice surprise thanks to the clean solution the ORM provided. Thx all

Answer 1

This is a very cool scenario to show off one feature of EntityFramework!

You could have a single table product, and a type column that defines the type of product.
Then in your Entity Data Model you define a base entity Product, and you create 2 derived entities HardwareProduct and ArtProduct. You can add a Condition on the Mapping for your child Entity like so :

EDIT : You should read When ProductTypeID = 1, but I’m lazy to redo the screenshot now 😉

See the “When ProductTypeID = 1 “

There 🙂