public virtual JsonResult Create([DataSourceRequest] DataSourceRequest request, TaskViewModel task)
        {
            if (ModelState.IsValid)
            {
                taskService.Insert(task, ModelState);
            }

            return Json(new[] { task }.ToDataSourceResult(request, ModelState));
        }
        public virtual JsonResult Update([DataSourceRequest] DataSourceRequest request, TaskViewModel task)
        {
            //example custom validation:
            if (task.Start.Hour < 8 || task.Start.Hour > 22)
            {
                ModelState.AddModelError("start", "Start date must be in working hours (8h - 22h)");
            }

            if (ModelState.IsValid)
            {
                taskService.Update(task, ModelState);
            }

            return Json(new[] { task }.ToDataSourceResult(request, ModelState));
        }