ModelState.AddModelError for Ajax loaded partials - ajax

Question

I have a partial view on my main page that loads a form, the model is below:
public class CreateRequestViewModel
{
[Required]
public short ClientId { get; set; }
[Required]
public Guid SystemId { get; set; }
[Required]
public string RequestedUsername { get; set; }
public string TicketReference { get; set; }
public string Notes { get; set; }
public List<SelectListItem> Clients { get; set; }
public List<SelectListItem> Systems { get; set; }
}
This is the partial view:
#model Models.CreateRequestViewModel
#Html.AntiForgeryToken()
#Html.ValidationSummary(true, "", new { #class = "text-danger" })
<div class="row">
<div class="col-lg-4 col-md-4 col-sm-12">
<h1>Create a Request</h1>
</div>
<div class="col-lg-8 col-md-8 col-sm-12 right">
<div class="form-group">
#Html.DropDownListFor(m => m.ClientId, Model.Clients, htmlAttributes: new { #class = "form-control form-control-lg", #id = "ClientSelect" })
#Html.ValidationMessageFor(m => m.ClientId, "", htmlAttributes: new { #class = "text-danger" })
</div>
<div class="form-group">
#Html.DropDownListFor(m => m.SystemId, Model.Systems, htmlAttributes: new { #class = "form-control form-control-lg", #id = "ClientSystemSelect" })
#Html.ValidationMessageFor(m => m.SystemId, "", htmlAttributes: new { #class = "text-danger" })
</div>
<div class="form-group">
#Html.TextBoxFor(m => m.RequestedUsername, htmlAttributes: new { #class = "form-control form-control-lg", #placeholder = "Username" })
#Html.ValidationMessageFor(m => m.RequestedUsername, "", htmlAttributes: new { #class = "text-danger" })
</div>
<div class="form-group">
#Html.TextBoxFor(m => m.TicketReference, htmlAttributes: new { #class = "form-control form-control-lg", #placeholder = "Ticket reference" })
</div>
<div class="form-group">
#Html.TextAreaFor(m => m.Notes, htmlAttributes: new { #class = "form-control form-control-lg", #rows = 3, #placeholder = "Notes..." })
</div>
<input type="Submit" class="btn btn-secondary btn-block send-request" value="Submit" name="">
</div>
</div>
This is how I'm loading the page:
<div class="container">
<div class="row">
<div class="col-lg-6">
<form asp-action="CreateRequest" asp-controller="Access"
data-ajax="true"
data-ajax-method="POST"
data-ajax-mode="replace"
data-ajax-update="#createRequest">
<div id="createRequest">
#await Html.PartialAsync("_CreateRequest", Model.CreateRequestModel)
</div>
</form>
</div>
</div>
</div>
With the model as it is and using the unobtrusive javascript, leaving the RequestedUsername blank for example will result in the form not being submitted and a validation message appearing for it. This is great.
However, I have a requirement to check the form data against entries in a database first and throw an error if there's an existing record. I thought that, with all the client side validation passing, I'd use ModelState.AddModelError in the controller like so:
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult CreateRequest(CreateRequestViewModel model)
{
if(model.RequestedUsername == "someincorrectvalue"){ //actual logic removed for brevity
ModelState.AddModelError("RequestedUsername", "Already in use");
}
if(!ModelState.IsValid)
{
//reset lists on model, removed
return PartialView("_CreateRequest", model);
}
_logger.LogInformation("CreateRequest successful");
return RedirectToAction(nameof(Index));
}
However, if I use ModelState.AddModelError, the return PartialView("_CreateRequest", model) call ends up reloading the whole page as if it's returning a full View.
I'm at a loss as to why this is happening. The difference I can see is that i'm adding a ModelState error inside the controller, whereas validation is happening client side otherwise.
Anyone have an idea?

Answer 1

So, this turned out to be a combination of problems. To begin with, the unobtrusive Ajax scripts I had within my solution were not performing. I don't know why but I replaced them with one from the CDN: https://ajax.aspnetcdn.com/ajax/jquery.unobtrusive-ajax/3.2.5/jquery.unobtrusive-ajax.min.js
That solved the problem of the whole page reloading instead of the partial being returned via unobtrusive ajax.
The second problem was that, on success, I was redirecting to the Index controller action instead of returning a Partial again. This was causing the entire Index page to be rendered inside the div i'd chosen as my ajax target. My controller action now looks like this:
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult CreateRequest(CreateRequestViewModel model)
{
if(model.RequestedUsername == "someincorrectvalue"){ //actual logic removed for brevity
ModelState.AddModelError("RequestedUsername", "Already in use");
}
if(!ModelState.IsValid)
{
//reset lists on model, removed
return PartialView("_CreateRequest", model);
}
_logger.LogInformation("CreateRequest successful");
// reset lists on model, removed
ModelState.Clear(); // get rid ofany model details to make way for a new request
return PartialView("_CreateRequest", model);
}