ValidationSummary displays duplicate messages

Question

If two of textboxes fail validation at once then the ValidationSummary displays the same message twice.

Am I doing something wrong? Or is there a setting I can change to hide duplicate messages?

 

I have broken it down to the simplest example:

View:

@model MyModel
@Html.ValidationSummary()
@Html.TextBoxFor(model => model.A)
@Html.TextBoxFor(model => model.B)

Model:

public class MyModel : IValidatableObject
{
    public int A { get; set; }
    public int B { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
        //Some logic goes here.        
        yield return new ValidationResult("Validation failed", new[] { "A", "B" });
    }
}

Result:

Answer 1

They are not duplicate from the point of view of ValidationSummary - you are assigning model state error to both fields A and B, so there must be 2 errors in validation summary. It doesnt "know" that they are the same.

Easy solutions :

• assign model only to one of them
• exclude property-assigned errors from summary - Html.ValidationSummary(true)

A little bit harder solution :

• make your own ValidationSummary helper, call standard validation summary logic in it, and then filter the result in "select distinct" way (linq is your friend here).

EDIT:

something like this for example :

public static class ValidationExtensions
{
    public static MvcHtmlString FilteredValidationSummary(this HtmlHelper html)
    {
        // do some filtering on html.ViewData.ModelState 
        return System.Web.Mvc.Html.ValidationExtensions.ValidationSummary(html);
    }
}

Answer 2

Whack this is your View

<ul class="validation-summary-errors">
    @{
        string errorMessage = "", previousError = "";
        foreach (ModelState modelState in (ViewContext.ViewData.ModelState.Values)){

            foreach (ModelError modelError in modelState.Errors)
            {
                errorMessage = modelError.ErrorMessage;
                if (errorMessage != previousError)
                {
                    <li>@modelError.ErrorMessage</li>
                    previousError = modelError.ErrorMessage;
                }                            
            }    
        }
    }
</ul>

You might be able to improve this as it only works when 2 consecutive errors are the same, if it jumbles the order this might not work, but this will start you off. I suppose you could build an array of error messages and check the error off it each run through, but this solution seems to work most of the time.