ASP.Net MVC 3 JSON Model Binding and server side model validation mixed with client side validation

Question

I\'ve been playing with the new MVC3 Json Model Binding and it\'s quite nice.

Currently, I can post JSON to controller and bind it. Model Validation occurs nicely too.

Answer 1

Thanks for this solution. I improved on it a bit by passing a dictionary so that you can use the unobtrusive javascript to put the validation on the individual fields instead of a summary by referencing the key of the dictionary.

    private Dictionary<string, string> GetModelStateErrorsAsString(ModelStateDictionary state)
    {
        Dictionary<string, string> errors = new Dictionary<string, string>();
        foreach (var key in ModelState.Keys)
        {
            var error = ModelState[key].Errors.FirstOrDefault();
            if (error != null)
            {
                errors.Add(key, error.ErrorMessage);
            }
        }
        return errors;
    }

Answer 2

@Junto and @Jamey777, you both pass the ModelState to your error function but then you use the global variable instead of the parameter.

and why dont you just use a little linq like

    private Dictionary<string, string> GetModelStateErrorsAsString()
    {
        return ModelState.Where(x=> x.Value.Errors.Any())
            .ToDictionary(x => x.Key, x => x.Value.Errors.First().ErrorMessage);
    }

Answer 3

The following example works for me when using unobtrusive JavaScript in MVC3. I'm doing something very similar. Given the following JsonResponse class:

public enum Status
{
    Ok,
    Error
}

public class JsonResponse
{
    public Status Status { get; set; }
    public string Message { get; set; }
    public List<string> Errors { get; set; }
}

My controller can have a method thus:

[HttpPost]
public ActionResult Login(UserLoginModel model)
{
    JsonResponse res = new JsonResponse();

    if (!ModelState.IsValid)
    {
        res.Status = Status.Error;
        res.Errors = GetModelStateErrorsAsString(this.ModelState);
        res.Message = "Oh dear, what have you done. Check the list of errors dude!";
    }
    else
    {
        // Save it here...

        // Return success
        res.Status = Status.Ok;
        res.Message = "Everything was hunky dory";
    }            

    return Json(res);
}

And the ModelStateDictionary can be enumerated for the errors as so:

private List<string> GetModelStateErrorsAsString(ModelStateDictionary state)
{
    List<string> errors = new List<string>();

    foreach (var key in ModelState.Keys)
    {
        var error = ModelState[key].Errors.FirstOrDefault();
        if (error != null)
        {
            errors.Add(error.ErrorMessage);
        }
    }

    return errors;
}

Then in my view I can have the following JSON POST:

<script type="text/javascript">
$("form").submit(function (evt) {
    // validate
    $('form').valid();

    // extract values to submit         
    var form = $(this),
        username = form.find("[name=Username]").val(),
        password = form.find("[name=Password]").val(),
        json = JSON.stringify({
            Username: username,
            Password: password
        });

    $.ajax({
        url: form.attr("action"),
        type: 'POST',
        contentType: 'application/json; charset=utf-8',
        dataType: 'json',
        data: json,
        success: function (result) {
            alert(result.Message);
        }
    });

    // stop form submitting
    evt.preventDefault();
});
</script>

I'm using jQuery.tmpl to display the errors. I have excluded that from this example though.