private void loadOperationProductType_Completed(object sender, EventArgs e)
        {
            ProductTypeEntityList.Clear();
            LoadOperation loadOperation = sender as LoadOperation;

            foreach (ProductManager.Web.Model.product_type product_type in loadOperation.Entities)
            {
                ProductTypeEntity productTypeEntity = new ProductTypeEntity();
                productTypeEntity.ProductType = product_type;
                productTypeEntity.Update();
                ProductTypeEntityList.Add(productTypeEntity);
            }
            UpdateChanged("ProductTypeEntityList");
            IsBusy = false;
        }