Extend Validation Summary HTML Helper to remove duplicate error messages - asp.net-mvc

Question

I have a scenario where 1 of 10 fields needs to be completed. When I add an error to each of the 10 properties, this results in the same error message appearing in the validation summary 10 times.
I have looked at this ValidationSummary displays duplicate messages
public static MvcHtmlString UniqueValidationSummary(this HtmlHelper html, bool excludePropertyErrors)
{
// do some filtering on html.ViewData.ModelState
return System.Web.Mvc.Html.ValidationExtensions.ValidationSummary(html, excludePropertyErrors);
}
But I am not sure how to actually get it working. When the extension function is run on page load html.ViewData.ModelState is valid and has no messages.
How can I strip out any duplicate error messages via this extension?

Answer 1

You have to write helper method that the following code.
public static IHtmlString UniqueValidationSummary(ModelStateDictionary ms)
{
var resultHtml = new StringBuilder();
resultHtml.Append("<div class=\"validation-summary-errors text-danger\" data-valmsg-summary=\"true\">");
resultHtml.Append("<ul>");
var isError = false;
var knownValues = new HashSet<string>();
foreach (var key in ms.Keys)
{
foreach (var e in ms[key].Errors)
{
isError = true;
if (!knownValues.Contains(e.ErrorMessage))
{
resultHtml.Append("<li>" + e.ErrorMessage + "</li>");
knownValues.Add(e.ErrorMessage);
}
}
}
if (!isError) return null;
resultHtml.Append("</ul>");
resultHtml.Append("</div>");
return new HtmlString(resultHtml.ToString());
}
And then, you can use helper method from view(.cshtml).
#MyHelper.UniqueValidationSummary(ViewData.ModelState);

Answer 2

I wouldn't usually recommend doing this but in some cases it might be needed.
I recently ran into a similar problem and needed to do the same.
Instead of trying to parse the ModelState in razor view, i did it in the controller, before returning the view. Here is the extension i used:
(Please Note that this hasnt been extensively tested, but seems to be working - i just wrote it)
using System.Collections.Generic;
using System.Linq;
using System.Web.Mvc;
namespace WebApplication.Common
{
public static class ModelStateExtension
{
public static void RemoveDuplicateErrorMessages(this ModelStateDictionary modelStateDictionary)
{
//Stores the error messages we have seen
var knownValues = new HashSet<string>();
//Create a copy of the modelstatedictionary so we can modify the original.
var modelStateDictionaryCopy = modelStateDictionary.ToDictionary(
element => element.Key,
element => element.Value);
foreach (var modelState in modelStateDictionaryCopy)
{
var modelErrorCollection = modelState.Value.Errors;
for(var i = 0 ; i < modelErrorCollection.Count ; i++)
{
//Check if we have seen the error message before by trying to add it to the HashSet
if (!knownValues.Add(modelErrorCollection[i].ErrorMessage))
{
modelStateDictionary[modelState.Key].Errors.RemoveAt(i);
}
}
}
}
}
}
You simple need to call the extension on your ModelState before returning the view:
using WebApplication.Common;
if (!ModelState.IsValid)
{
//viewModel code omitted
ModelState.AddModelError("0", "Server Side Validation failed");
ModelState.RemoveDuplicateErrorMessages();
return View(viewModel);
}