ASP.Net MVC Using AddModelError with multiple ValidationSummary for querystring validation

Following the helpful information I was given by @GSerg, I thought I'd share my resolution.

So instead of having two forms within the same view, I split each form into two separate partial views and called each from within the main view...

@Html.Action("_RequestPartial")
@Html.Action("_LoginPartial")

Each partial view would contain the model to pass to it and a Html.BeginForm with a Html.ValidationSummary() inside.

Then within the Controller, set up the code to return the view as normal (in this case for the Index view)...

[HttpGet]
public ActionResult Index()
{
     return View();
}

Then for the partial views, set up a PartialViewResult for each partial view annotated with ChildActionOnly...

[ChildActionOnly]
public PartialViewResult _RequestPartial()
{
      ... code that populates model you want to pass ...

      return PartialView(model);
}

[ChildActionOnly]
public PartialViewResult _LoginPartial()
{
      ... code that populates model you want to pass ...

      return PartialView(model);
}

Hope this helps someone.

To show the specific validation message, please see the snippet code below. Controller :

[HttpGet]
        public ActionResult Index()
        {
            ModelState.AddModelError("Error1", "Querystring error");
            return View(new SampleViewModel());
        }

View :

@Html.ValidationMessage("Error1")

Just tried to create a fiddle to get a complete picture. https://dotnetfiddle.net/GoMMhy