public abstract class Base
        {
            public string A { get; set; }
        }

        public class T1 : Base
        {
            public string B { get; set; }
        }


        [Test]
        public void ProjectAfterOfTypeTest()
        {
            var server = MongoServer.Create(mongo.WriterConnectionString);
            var db = server.GetDatabase(mongo.Database);
            var collection = db.GetCollection<Base>("ProjectTest");

            var t1 = new T1 { A = "T1.A", B = "T1.B" };
        
            collection.Insert(t1);
        
            var query = from t in collection.AsQueryable().OfType<T1>() select t.B;
            var results = query.ToList();
            Assert.That(results.Count, Is.EqualTo(1));
            Assert.That(results[0], Is.EqualTo("T1.B"));
        }