private void main_category_query()
 {
     sql_object sql_obj = new sql_object();
     SqlDataReader dataReader = sql_obj.get_category_query();
     main_category.DataSource = dataReader;
     main_category.DataValueField = "id";
     main_category.DataTextField = "Category";
     main_category.DataBind();
     sql_obj.close_connection();
 }