Question

I have a couple of classes (for this example anyway) that use code first with the entity framework to connect to the database.

public class Customer
{
    [Key]
    public long CustomerId { get; set; }
    public string CompanyName { get; set; }
    ...
    public virtual List<Contact> Contacts { get; set; }
}

public class Contact
{
    [Key]
    public long ContactId { get; set; }
    public string Forename { get; set; }
    ...
    public long CustomerId { get; set; }

    public virtual Customer Customer { get; set; }
}

When I hook these up in my context class directly to the db the foreign key relationships hook up fine and I can access the collection of contacts from within the customer class.

class RemoteServerContext : DbContext 
{
    public DbSet<Customer> Customers { get; set; }
    public DbSet<Contact> Contacts { get; set; }
    ...
}

My problem is that these database tables are used by various different systems and are massive. In order to increase efficiency I have overridden the default behaviour to point at a view (and also a stored proc elsewhere) rather than directly at the table.

    public IEnumerable<Customer> Customers ()
    {
        return Database.SqlQuery<Customer>("SELECT * FROM vw_CustomerList");
    }

    public IEnumerable<Contact> Contacts()
    {
        return Database.SqlQuery<Contact>("SELECT * FROM vw_ContactsList");
    }

I have made sure that in each of the views I have included the foreign key fields: CustomerId and ContactId.

When I do this however the class joins appear to be lost – there’s always a null when I drill into either of the objects where it should be pointing to the other one. I have tried to set up what the foreign key field should point to but this doesn’t seem to help either.

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        modelBuilder.Entity<Contact>().HasRequired(p => p.Customer)
            .WithMany()
            .HasForeignKey(k => k.CustomerId);
    }

Is there a way to establish the connection when overriding the default behaviour?

Answer 1

There is no overriding in this case. If you removed

public DbSet<Customer> Customers { get; set; }

and replaced it with

public IEnumerable<Customer> Customers ()
{
    return Database.SqlQuery<Customer>("SELECT * FROM vw_CustomerList");
}

you have completely changed the behavior. The first uses entities and full power of EF. The second is only helper to execute custom SQL. Second without first or without defining entity in OnModelCreating doesn’t use Customer as mapped entity at all – it uses it as any normal class (only mapped entities can use features like lazy loading).

Because your Customer is now mapped to view you cannot use your former Customer class used with table. You must define mapping of Customer to a view by cheating EF:

modelBuilder.Entity<Customer>().ToTable("vw_ContactsList"); // EF code fist has no view mapping

Once you have this you can try again using:

public DbSet<Customer> Customers { get; set; }

Unless your view is updatable you will get exception each time you try to add, update or delete any customer in this set. After mapping relation between Customer and Contact mapped to views your navigation properties should hopefully work.

The problem with SqlQuery is the way how it works. It returns detached entities. Detached entities are not connected to the context and they will not lazy load its navigation properties. You must manually attach each Customer instance back to context and to do that you again need DbSet.