Entity Framework - Selective Condition on Included Navigation Property

Question

Assume I have these simplified EF generated entities...

public class PurchaseOrder
{
     public int POID {get;set;}
     public int OrderID         


        

Answer 1

You can't. EF doesn't allow conditions for eager loading. You must either use multiple queries like:

var pos = from p in context.PurchaseOrders.Include("Order")
          where ...
          select p;
var items = from i in context.Items
            join o in context.Orders on new { i.OrderId, i.VendorId} 
               equals new { o.OrderId, o.PurchaseOrder.VendorId }
            where // same condition for PurchaseOrders
            select i;

Or you can use projection in single query:

var data = from o in context.Orders
           where ...
           select new
              {
                  Order = o,
                  PurchaseOrder = o.PurchaseOrder,
                  Items = o.Items.Where(i => i.VendorId == o.PurchaseOrder.VendorId)
              };