Question

i have a product manager application i’m trying to design using interfaces. a product can be 1 of 2 types Print or Online. i’d like to be able do the usual CRUD operations on it. i’m using Entity Framework but i came across a snag when building the interface.

For example I went to add my first method for the interface AddProduct(Product productToCreate). What type do I use for the Product since my entites are from Entity Framework? So I created an intermediate object call Product to transfer the Entity Framework object into it so it could fit in the interface. Is that right? Please advise.

class EFPrint
{
    //Entity Framework object
    public int PrintId { get; set; }
    public string Product { get; set; }
    public string Code { get; set; }
}

class EFOnline
{
    //Entity Framework object
    public int OnlineId { get; set; }
    public string Product { get; set; }
    public string Code { get; set; }
}

class Product
    {
    public int Id { get; set; }
    public string Product { get; set; }
    public string Code { get; set; }
    }

interface IProductManagerService
{
    void AddProduct(Product product);
}

class PrintService : IProductManagerService
{

    public void AddProduct(Product product)
    {
        throw new NotImplementedException();
    }
}

class OnlineService : IProductManagerService
{

    public void AddProduct(Product product)
    {
        throw new NotImplementedException();
    }
}

Answer 1

Entity Framework allows you to work with bases classes. You should create a base Product class, have the OnlineProduct and PrintProduct inherit from Product:

public class Product { ... }
public class Online : Product { ... }
public class Print : Product { ... }

In your DbContext, instead of having a DbSet for each type, you should have a single DbSet for Product, and just add accessors in order to retrieve only products from a specific type:

public class ProductsContext : DbContext
{
    public DbSet<Product> Products { get; set; }

    public IQueryable<Online> OnlineProducts
    {
        get
        {
            return Products.OfType<Online>();
        }
    }

    public IQueryable<Print> PrintProducts
    {
        get
        {
            return Products.OfType<Print>();
        }
    }
}