Pass selected item from drop down list to viewmodel - asp.net-mvc-4

Question

I have four controls on the page, a simple form with first and last names, date of birth and this drop down that contains some names of countries. When I make changes to the these controls I am able to see those changes in my viewModel that is passed in as a parameter in the SavePersonDetails POST below, but I never see the LocationId updated in that view model and I am not sure why.
This is what I have in my markup, Index.cshtml:
#model Mvc4withKnockoutJsWalkThrough.ViewModel.PersonViewModel
#using System.Globalization
#using Mvc4withKnockoutJsWalkThrough.Helper
#section styles{
#Styles.Render("~/Content/themes/base/css")
<link href="~/Content/Person.css" rel="stylesheet" />
}
#section scripts{
#Scripts.Render("~/bundles/jqueryui")
<script src="~/Scripts/knockout-2.1.0.js"></script>
<script src="~/Scripts/knockout.mapping-latest.js"></script>
<script src="~/Scripts/Application/Person.js"></script>
<script type="text/javascript">
Person.SaveUrl = '#Url.Action("SavePersonDetails", "Person")';
Person.ViewModel = ko.mapping.fromJS(#Html.Raw(Json.Encode(Model)));
var userObject = '#Html.Raw(Json.Encode(Model))';
var locationsArray = '#Html.Raw(Json.Encode(Model.Locations))';
var vm = {
user : ko.observable(userObject),
availableLocations: ko.observableArray(locationsArray)
};
ko.applyBindings(vm);
</script>
}
<form>
<p data-bind="with: user">
Your country:
<select data-bind="options: $root.availableLocations, optionsText: 'Text', optionsValue: 'Value', value: LocationID, optionsCaption: 'Choose...'">
</select>
</p>
</form>
This is my View Model:
public class PersonViewModel
{
public int Id { get; set; }
public string FirstName { get; set; }
public string LastName { get; set; }
public DateTime DateOfBirth { get; set; }
public string LocationId { get; set; }
public IEnumerable<SelectListItem> Locations { get; set; }
}
I have a simple controller that loads my Person and a drop down list containing three countries.
private PersonViewModel _viewModel;
public ActionResult Index()
{
var locations = new[]
{
new SelectListItem { Value = "US", Text = "United States" },
new SelectListItem { Value = "CA", Text = "Canada" },
new SelectListItem { Value = "MX", Text = "Mexico" },
};
_viewModel = new PersonViewModel
{
Id = 1,
FirstName = "Test",
LastName = "Person",
DateOfBirth = new DateTime(2000, 11, 12),
LocationId = "", // I want this value to get SET when the user changes their selection in the page
Locations = locations
};
_viewModel.Locations = locations;
return View(_viewModel);
}
[HttpPost]
public JsonResult SavePersonDetails(PersonViewModel viewModel)
{
int id = -1;
SqlConnection myConnection = new SqlConnection("server=myMachine;Trusted_Connection=yes;database=test;connection timeout=30");
try
{
// omitted
}
catch (Exception e)
{
Console.WriteLine(e.ToString());
}
finally
{
myConnection.Close();
}
return Json(id, "json");
}
Lastly, here is my Person.js file, I am using knockout
var Person = {
PrepareKo: function () {
ko.bindingHandlers.date = {
init: function (element, valueAccessor, allBindingsAccessor, viewModel) {
element.onchange = function () {
var observable = valueAccessor();
observable(new Date(element.value));
}
},
update: function (element, valueAccessor, allBindingsAccessor, viewModel) {
var observable = valueAccessor();
var valueUnwrapped = ko.utils.unwrapObservable(observable);
if ((typeof valueUnwrapped == 'string' || valueUnwrapped instanceof String) && valueUnwrapped.indexOf('/Date') === 0) {
var parsedDate = Person.ParseJsonDate(valueUnwrapped);
element.value = parsedDate.getMonth() + 1 + "/" + parsedDate.getDate() + "/" + parsedDate.getFullYear();
observable(parsedDate);
}
}
};
},
ParseJsonDate: function (jsonDate) {
return new Date(parseInt(jsonDate.substr(6)));
},
BindUIwithViewModel: function (viewModel) {
ko.applyBindings(viewModel);
},
EvaluateJqueryUI: function () {
$('.dateInput').datepicker();
},
RegisterUIEventHandlers: function () {
$('#Save').click(function (e) {
// Check whether the form is valid. Note: Remove this check, if you are not using HTML5
if (document.forms[0].checkValidity()) {
e.preventDefault();
$.ajax({
type: "POST",
url: Person.SaveUrl,
data: ko.toJSON(Person.ViewModel),
contentType: 'application/json',
async: true,
beforeSend: function () {
// Display loading image
},
success: function (result) {
// Handle the response here.
if (result > 0) {
alert("Saved");
} else {
alert("There was an issue");
}
},
complete: function () {
// Hide loading image.
},
error: function (jqXHR, textStatus, errorThrown) {
// Handle error.
}
});
}
});
},
};
$(document).ready(function () {
Person.PrepareKo();
Person.BindUIwithViewModel(Person.ViewModel);
Person.EvaluateJqueryUI();
Person.RegisterUIEventHandlers();
});
As you can see, I have the data in the page but none of them show as selected

Answer 1

Your solution is overly complex and is leading to certain weirdness with your data. Instead of trying to patch the Titanic, your best bet is to start over and simplify:
Your page's model contains all the information you need. There's no need to try to create two totally separate view models to work with the user data versus locations. With the mapping plugin, you can specify different "view models" for various objects in your main view model, and there's a simpler pattern that can be followed to set all that up. Here's what I would do:
// The following goes in external JS file
var PersonEditor = function () {
var _init = function (person) {
var viewModel = PersonEditor.PersonViewModel(person);
ko.applyBindings(viewModel);
_wireEvents(viewModel);
}
var _wireEvents = function (viewModel) {
// event handlers here
}
return {
Init: _init
}
}();
PersonEditor.PersonViewModel = function (person) {
var mapping = {
'Locations': {
create: function (options) {
return new PersonEditor.LocationViewModel(options.data)
}
}
}
var model = ko.mapping.fromJS(person, mapping);
// additional person logic and observables
return model;
}
PersonEditor.LocationViewModel = function (location) {
var model = ko.mapping.fromJS(location);
// additional location logic and observables
return model;
}
// the following is all you put on the page
<script src="/path/to/person-editor.js"></script>
<script>
$(document).ready(function () {
var person = #Html.Raw(#Json.Encode(Model))
PersonEditor.Init(person);
});
</script>
Then all you need to bind the select list to the locations array is:
<p>
Your country:
<select data-bind="options: Locations, optionsText: 'Text', optionsValue: 'Value', value: LocationId, optionsCaption: 'Choose...'">
</select>
</p>

Answer 2

Based on your updated question, do this.
1.We do not need locationsArray actually. Its already in user.Locations (silly me)
2.On Index.cshtml, page change the JavaScript like this.
var userObject = #Html.Raw(Json.Encode(Model)); // no need for the quotes here
jQuery(document).ready(function ($) {
Person.PrepareKo();
Person.EvaluateJqueryUI();
Person.RegisterUIEventHandlers();
Person.SaveUrl = "#Url.Action("SavePersonDetails", "Knockout")";
Person.ViewModel = {
user : ko.observable(userObject)
};
Person.BindUIwithViewModel(Person.ViewModel);
});
3.On your Person.js page, inside RegisterUIEventHandlers #Save button click event, do this.
$('#Save').click(function (e) {
var updatedUser = Person.ViewModel.user();
updatedUser.Locations.length = 0; // not mandatory, but we don't need to send extra payload back to server.
// Check whether the form is valid. Note: Remove this check, if you are not using HTML5
if (document.forms[0].checkValidity()) {
e.preventDefault();
$.ajax({
type: "POST",
url: Person.SaveUrl,
data: ko.toJSON(updatedUser), // Data Transfer Object
contentType: 'application/json',
beforeSend: function () {
// Display loading image
}
}).done(function(result) {
// Handle the response here.
if (result > 0) {
alert("Saved");
} else {
alert("There was an issue");
}
}).fail(function(jqXHR, textStatus, errorThrown) {
// Handle error.
}).always(function() {
// Hide loading image.
});
}
});
5.Finally, our markup
<p data-bind="with: user">
Your country:
<select data-bind="options: Locations,
optionsText: 'Text',
optionsValue: 'Value',
value: LocationId,
optionsCaption: 'Choose...'">
</select>
</p>
On an unrelated side-note,
The jqXHR.success(), jqXHR.error(), and jqXHR.complete() callbacks are
deprecated as of jQuery 1.8. To prepare your code for their eventual
removal, use jqXHR.done(), jqXHR.fail(), and jqXHR.always() instead.