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 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

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

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

First 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.Any());         }         return null;     } } 

Then call that extension method and 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());     } }