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: ( Returning a list of keys with ModelState errors)

var errorK         


        

Answer 1

You can put anything you want to inside the select clause:

var errorList = (from item in ModelState
        where item.Value.Errors.Any() 
        select item.Value.Errors[0].ErrorMessage).ToList();

EDIT: You can extract multiple errors into separate list items by adding a from clause, like this:

var errorList = (from item in ModelState.Values
        from error in item.Errors
        select error.ErrorMessage).ToList();

Or:

var errorList = ModelState.Values.SelectMany(m => m.Errors)
                                 .Select(e => e.ErrorMessage)
                                 .ToList();

2^nd EDIT: You're looking for a Dictionary<string, string[]>:

var errorList = ModelState.ToDictionary(
    kvp => kvp.Key,
    kvp => kvp.Value.Errors.Select(e => e.ErrorMessage).ToArray()
);

Answer 2

Variation with return type instead of returning IEnumerable

public static class ModelStateHelper
{
    public static IEnumerable<KeyValuePair<string, string[]>> 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.Any());
        }

        return null;
    }
}

Answer 3

There are lots of different ways to do this that all work. Here is now I do it...

if (ModelState.IsValid)
{
    return Json("Success");
}
else
{
    return Json(ModelState.Values.SelectMany(x => x.Errors));
}

Answer 4

Take a look at System.Web.Http.Results.OkNegotiatedContentResult.

It converts whatever you throw into it to JSON.

So I did this

var errorList = ModelState.ToDictionary(kvp => kvp.Key.Replace("model.", ""), kvp => kvp.Value.Errors[0].ErrorMessage);

return Ok(errorList);

This resulted in:

{
  "Email":"The Email field is not a valid e-mail address."
}

I am yet to check what happens when there is more than one error for each field but the point is the OkNegoriatedContentResult is brilliant!

Got the linq/lambda idea from @SLaks

Answer 5

Why not return the original ModelState object to the client, and then use jQuery to read the values. To me it looks much simpler, and uses the common data structure (.net's ModelState)

to return the ModelState as Json, simply pass it to Json class constructor (works with ANY object)

C#:

return Json(ModelState);

js:

        var message = "";
        if (e.response.length > 0) {
            $.each(e.response, function(i, fieldItem) {
                $.each(fieldItem.Value.Errors, function(j, errItem) {
                    message += errItem.ErrorMessage;
                });
                message += "\n";
            });
            alert(message);
        }

Answer 6

  List<ErrorList> Errors = new List<ErrorList>(); 


        //test errors.
        var modelStateErrors = this.ModelState.Keys.SelectMany(key => this.ModelState[key].Errors);

        foreach (var x in modelStateErrors)
        {
            var errorInfo = new ErrorList()
            {
                ErrorMessage = x.ErrorMessage
            };
            Errors.Add(errorInfo);

        }

if you use jsonresult then return

return Json(Errors);

or you can simply return the modelStateErrors, I havent tried it. What I did is assign the Errors collection to my ViewModel and then loop it..In this case I can return my Errors via json. I have a class/model, I wanted to get the source/key but I'm still trying to figure it out.

    public class ErrorList
{
    public string ErrorMessage;
}