changed builder to assume that if the discriminator did not show up t…

…hen the class is the base class.

examples/Simple/Main.cs

@@ -81,6 +81,14 @@ public static void Main(string[] args)
                     collection.Save(circle);
                     collection.Save(sub);
 
+                    var superclass = (from item in db.GetCollection<MyClass>("MyClass").Linq()
+                                where item.Corners > 1
+                                select item.Corners).ToList();
+
+                    var subclass = (from item in db.GetCollection<SubClass>("MyClass").Linq()
+                                    where item.Ratio > 1
+                                    select item.Corners).ToList();
+
                     Console.WriteLine("Count by LINQ on typed collection: {0}", collection.Linq().Count(x => x.Corners > 1));
                     Console.WriteLine("Count by LINQ on typed collection2: {0}", db.GetCollection<SubClass>().Linq().Count(x => x.Corners > 1));
                     //Console.WriteLine("Count by LINQ on typed collection3: {0}", db.GetCollection<SubClass>().Count(new { Corners = Op.GreaterThan(1) }));

source/MongoDB/Serialization/Builders/PolymorphicClassMapBuilder.cs

@@ -38,7 +38,10 @@ public void AddProperty(string name, object value)
         public object BuildObject()
         {
             if (_concreteEntityBuilder == null)
-                throw new Exception("Discriminator did not show up.");
+            {
+                //we'll assume that this is the root class in the hierarchy.
+                _concreteEntityBuilder = new ConcreteClassMapBuilder(_classMap);
+            }
 
             return _concreteEntityBuilder.BuildObject();
         }