ASP.NET MVC How to convert ModelState errors to json

Question

How do you get a list of all ModelState error messages? I found this code to get all the keys: ( http://stackoverflow.com/questions/888521/returning-a-list-of-keys-with-modelstate-errors)

var errorKeys = (from item in ModelState
        where item.Value.Errors.Any() 
        select item.Key).ToList();

But how would I get the error messages as a IList or IQueryable?

I could go:

foreach (var key in errorKeys)
{
    string msg = ModelState[error].Errors[0].ErrorMessage;
    errorList.Add(msg);
}

But thats doing it manually - surely there is a way to do it using LINQ? The .ErrorMessage property is so far down the chain that I don't know how to write the LINQ...

Answer 1

Here is the full implementation with all the pieces put together:

1st create an extension method:

public static class ModelStateHelper
{
    public static IEnumerable Errors(this ModelStateDictionary modelState)
    {
        if (!modelState.IsValid)
        {
            return modelState.ToDictionary(kvp => kvp.Key,
                kvp => kvp.Value.Errors.Select(e => e.ErrorMessage).ToArray()).Where(m => m.Value.Count() > 0);
        }
        return null;
    }
}

Then return the errors from the controller action (if any) as json:

            if (!ModelState.IsValid)
            {
                return Json(new { Errors = ModelState.Errors() }, JsonRequestBehavior.AllowGet);
            }

And then finally, show those errors on the clientside (in jquery.validation style, but can be easily changed to any other style)

function DisplayErrors(errors) {
    for (var i = 0; i < errors.length; i++) {
        $("<label for='" + errors[i].Key + "' class='error'></label>").html(errors[i].Value[0]).appendTo($("input#" + errors[i].Key).parent());
    }
}

Answer 2

ToDictionary is an Enumerable extension found in System.Linq packaged in the System.Web.Extensions dll http://msdn.microsoft.com/en-us/library/system.linq.enumerable.todictionary.aspx. Here's what the complete class looks like for me.

using System.Collections;
using System.Web.Mvc;
using System.Linq;

namespace MyNamespace
{
    public static class ModelStateExtensions
    {
        public static IEnumerable Errors(this ModelStateDictionary modelState)
        {
            if (!modelState.IsValid)
            {
                return modelState.ToDictionary(kvp => kvp.Key,
                    kvp => kvp.Value.Errors.Select(e => e.ErrorMessage).ToArray()).Where(m => m.Value.Count() > 0);
            }
            return null;
        }

    }

}