left outer join with devforce

      var op = Coroutine.Start(AsyncLeftOuterJoinQueryCore);
      op.Completed += (s, args) => {
        var queryResult = args.Result;
      };

   private IEnumerable<INotifyCompleted> AsyncLeftOuterJoinQueryCore() {
      var mgr = new EntityManager();
      
      //bring down categories
      var catQuery = mgr.Categories;
      var catOp = catQuery.ExecuteAsync();
      yield return catOp;

      //bring down products
      var prodQuery = mgr.Products;
      var prodOp = prodQuery.ExecuteAsync();
      yield return prodOp;

      var categories = catOp.Results;
      var products = prodOp.Results;

      var result = from c in categories
                   join p in products
                   on c equals p.Category into ps
                   from p in ps.DefaultIfEmpty()
                   select new { Category = c, ProductName = p == null ? "(No products)" : p.ProductName };
      
      yield return Coroutine.Return(result);
    }