to get data from datasource declared in aspx

 public bool OrderExists(int order_index) {
        DataView dv1 = (DataView)CategoriesDataSource.Select(new DataSourceSelectArguments());
        foreach( DataRow d in dv1.Table.Rows){
            if ((int)d["order_index"] == order_index) {
                gvMerchantCategoriesLabel.Text = "Update Not Successful, Order Index Already exists";
                gvMerchantCategoriesLabel.Style.Add("color", "#FF0000");
                return true;
            }

        }
        return false;
    }