ValidationMessage and ModelState.AddModelError not working

Question

I want to do cusotm validation and return false and show message in case of validation fail.

In controller below code is used to submit posted data to database.

       [HttpPost]
       public JsonResult SubmitDa(IList<AdViewModel> s, String section)
           {

            ...........
              ..........


            ModelState.AddModelError("MessageError", "Please enter AttendanceDate");

             JSONSubmit r = new JSONSubmit();
            r.ErrorCount = iError;
            r.errors = errors;

           return Json(r, JsonRequestBehavior.AllowGet);

       }

Below is the code in view file (cshtml)

       @Html.ValidationMessage("MessageError")  
        .....  

       $.AJAX call to `SubmitDa` controller's method.

Message is not appearing at "MessageError" validation message. please suggest me what is wrong here.

Thanks

Answer 1

If you want to use the modelstate for errors you shouldn't really be sending a JSON response. Having said that you can handle it by having the controller return JSON only in the case of success, and the page handles the response differently

IE:

[HttpPost]
public ActionResult SubmitDa(IList<AdViewModel> s, String section)
{

        ...........
          ..........


        ModelState.AddModelError("MessageError", "Please enter AttendanceDate");

         JSONSubmit r = new JSONSubmit();
        r.ErrorCount = iError;
        r.errors = errors;
       if (r.ErrorCount != 0)
           return Json(r, JsonRequestBehavior.AllowGet);

       return View("ViewName", s); // <-- just return the model again to the view,
                                   //     complete with modelstate!
}

on the page something like:

<script>

$("#buttonId").click({
   $.ajax({
     type: "POST",
     url: "PostBackURL",
     data: $("#formID").serialize(),
     success: function (response){
       //test for a property in the JSON response
       if(response.ErrorCount && response.ErrorCount == 0) 
       {
           //success! do whatever else you want with the response

       } else {
          //fail - replace the HTML with the returned response HTML.
          var newDoc = document.open("text/html", "replace");
          newDoc.write(response);
          newDoc.close();
       }

     }
   });
});

</script>