How to render errors to client? AngularJS/WebApi ModelState

Question

I'm building an AngularJS SPA application with WebApi for the backend. I am using attributes for model validation on the server, if validation fails this is what I return from the ModelState.

     {"Message":"The request is invalid.","ModelState":{"model.LastName":["Last Name must be at least 2 characters long."]}}

How do I then render this to the client with AngularJS?

      //Save User Info
    $scope.processDriverForm = function(isValid) {
        if (isValid) {
            //set button disabled, icon, text
            $scope.locked = true;
            $scope.icon = 'fa fa-spinner fa-spin';
            $scope.buttonText = 'Saving...';
            $scope.submitted = true;
            $scope.formData.birthDate = $scope.formData.birthMonth + '/' + $scope.formData.birthDay + '/' + $scope.formData.birthYear;
            $http({
                    method: 'POST',
                    url: 'api/Account/Register',
                    data: $.param($scope.formData),
                    headers: { 'Content-Type': 'application/x-www-form-urlencoded' } // set the headers so angular passing info as form data (not request payload)
                })
                .success(function (data) {
                    console.log(data);
                    toastr.success('User ' + $scope.formData.username + ' created!');
                    $scope.userForm.$setPristine();
                    $scope.formData = {};
                    //reset the button
                    $scope.locked = false;
                    $scope.icon = '';
                    $scope.buttonText = 'Save';
                    //reset validation submitted
                    $scope.submitted = false;
                })
                .error(function (data, response) {
                    console.log(data);
                    toastr.error('Ooops! There was an error creating the user. Try again and if the problem persists, contact Support.');
                    //reset the button
                    $scope.locked = false;
                    $scope.icon = '';
                    $scope.buttonText = 'Save';
                    $scope.submitted = false;

                    var resp = {};

                    var errors = [];
                    for (var key in resp.ModelState) {
                        for (var i = 0; i < resp.ModelState[key].length; i++) {
                            errors.push(resp.ModelState[key][i]);
                        }
                    }
                    $scope.errors = errors;

                });

        }
        else {
            toastr.warning('Invalid User Form, correct errors and try again.');
        }
    };

Answer 1

When making your call to your server, capture the error based upon the rejection of the $http promise.

Then in your controller I would suggest flattening the response to an array of errors upon handling of the error for display as shown in this fiddle example:

for (var key in resp.ModelState) {
    for (var i = 0; i < resp.ModelState[key].length; i++) {
        errors.push(resp.ModelState[key][i]);
    }
}

To put it all together:

// Post the data to the web api/service
$http.post(url, data)
    .success(successHandler)
    .error(function (response) {
        // when there's an error, parse the error
        // and set it to the scope (for binding)
        $scope.errors = parseErrors(response);
    });

//separate method for parsing errors into a single flat array
function parseErrors(response) {
    var errors = [];
    for (var key in response.ModelState) {
        for (var i = 0; i < response.ModelState[key].length; i++) {
            errors.push(response.ModelState[key][i]);
        }
    }
    return errors;
}