实体框架-自定义导航属性以抽象联接

Question

I have looked through similar questions here, but not seen this specific scenario.

Using EF 6 Code First, I have three tables, A, B and C. The relationship is A => B = 1:M, and B=>C = 1:1

The end result in this schema is that there is an implicit 1:M between A and C.

I do NOT want the consumer of the Entity Framework model to know about B. Ideally they would have a 1:M Navigation property from A to C (and I'd like to be able to surface this Entity Model through Web API and OData as IQueryable)

How could I do this?

If I add a custom [NotMapped] property to A which a collection of C, I have no way of populating C within the getter of that property because the entity doesn't know about its context.

Anyone have any ideas as to how to implement an IQueryable where A has a navigation property to C and B is 'abstracted' out of existence?

EDIT

Attempted to put the following into the code first entity A:

[NotMapped]
public ICollection<C> Cs
{
        get { return this.Bs.Select(b => b.C) as ICollection<C>; }
}

But got this error: The navigation property 'C' is not a declared property on type 'A'. Verify that it has not been explicitly excluded from the model and that it is a valid navigation property.

Thanks.

Answer 1

Here is an example.

public static class OrderDAL
{
    public static Order Get(int key)
    {
        using (var context = new AppContext())
        {
            var order = context.Orders.Include(a => a.OrderDetails.Select(b => b.Information)).FirstOrDefault(a => a.Id == key);
            // Fills C.
            order.OrderDetailAdditionalInformation = order.OrderDetails.Select(b => b.Information).ToArray();
            // Hides information about B.
            foreach (var information in order.OrderDetailAdditionalInformation)
            { information.OrderDetail = null; }
            order.OrderDetails = null;
            return order;
        }
    }
}
public class AppContext : DbContext
{
    public DbSet<Order> Orders { get; set; }
}
// A
public class Order
{
    public int Id { get; set; }
    public DateTime Date { get; set; }
    public ICollection<OrderDetail> OrderDetails { get; set; }
    [NotMapped]
    public ICollection<OrderDetailAdditionalInformation> OrderDetailAdditionalInformation { get; set; }
}
// B, one A many B
public class OrderDetail
{
    public int Id { get; set; }
    public int Qty { get; set; }
    public string Item { get; set; }
    public int OrderId { get; set; }
    public Order Order { get; set; }
    public OrderDetailAdditionalInformation Information { get; set; }
}
// C, one B one C
public class OrderDetailAdditionalInformation
{
    [ForeignKey("OrderDetail")]
    public int Id { get; set; }
    public int Width { get; set; }
    public int Height { get; set; }
    public int Long { get; set; }
    public OrderDetail OrderDetail { get; set; }
}