Question

I’m trying to associate two entity types in EF4, there is no foreign key available.

Is there any manual tweaks I can do to so when I load an instance of order I get something like:

order.orderID = 455
order.date = 2012-08-12
order.OrderItems = <List>OrderItem // OrderItem being the other entity I want to map on         order

I guess I’ll have to do this manually when I Select() an order and set it’s OrderItems property since no FKs are avail.

Am I on the right track ?

**EDIT:

I was able to create an association between orders and orderitems and here’s a Select() method I have for an order:

    public Order Select(long orderID)
    {
        using (var ctx = new BillingSystemEntities())
        {
            var res = from n in ctx.Orders
                      where n.OrderID == orderID
                      select n;
                 if (res.Count() == 0)
                    return null;
                else
                    return  res.First();
         }
    }

According to SQL Profiler, EF is not doing any JOIN on OrderItem table. I guess I need to load them into the OrderItems navigation property myself ?

Answer 1

You just need to include the OrderItems in your query:

public Order Select(long orderID)
{
    using (var ctx = new BillingSystemEntities())
    {
        var res = from n in ctx.Orders.Include("OrderItems")
                  where n.OrderID == orderID
                  select n;
        return res.FirstOrDefault();
    }
}

Also FirstOrDefault is more appropriate here than your Count()...First() construct because it hits the database only once while Count() and First() will issue a separate query each.

You can write it even more compact with:

public Order Select(long orderID)
{
    using (var ctx = new BillingSystemEntities())
    {
        return ctx.Orders.Include("OrderItems")
            .FirstOrDefault(n => n.OrderID == orderID);
    }
}