C# model to Javascript object- using knockout.js

Question

I'm trying to use knockout.js to perform add/remove operations on a server-side property. Here's what my C# Model looks like:

public class MyModel
{
    [Key]
    public int MyModelId { get; set; }

    [Required]
    public string Name { get; set; }

    private IEnumerable<string> _Items;

    [Required]
    public IEnumerable<string> Items
    {
        get { return _Items; }
        set { _Items = value; }
    }

    //Used to store in SQL database
    public string ItemsSQL
    {
        get { return _Items != null ? String.Join(";", _Items) : null; }
        set { _Items = value != null ? value.Split(';').ToList() : null; }
    }
}

Here's what my ViewModel looks like:

@model MyProject.Models.MyModel

<script src="@Url.Content("~/Scripts/jquery-1.5.1.min.js")" type="text/javascript"></script>
<script src="@Url.Content("~/Scripts/knockout-2.1.0.js")" type="text/javascript"></script>
<script type="text/javascript">
    @{
        var initialData = new JavaScriptSerializer().Serialize(Model);
    }
    var viewModel = {
        MyModel: ko.observable(@Html.Raw(initialData)),

        //Commented out on purpose
        //Items: ko.observableArray(this.MyModel.Items),

        addItem: function() { 
            this.MyModel.Items.push("");
        },

        removeItem: function(item) {
            this.MyModel.Items.remove(item);
        },
    };

    alert(JSON.stringify(@Html.Raw(initialData)));

    $(document).ready(function() {ko.applyBindings(viewModel); });
</script>

And Here's my view:

Name: <span data-bind="text: MyModel().Name"></span>
<br />
Items: <button data-bind="click: addItem">Add Item</button>

<table>
    <tbody data-bind="template: { name: 'itemTemplate', foreach: MyModel().Items}"></tbody>
</table>

<script type="text/html" id="itemTemplate">
    <tr>
        <td>
            <input data-bind="value: $data" />
            <a href="#" data-bind="click: function() { 
                                   viewModel.removeItem($data) }">Remove Item</a>
        </td>
    </tr>
</script>

This displays MyModel.Name along with each item in MyModel.Itemsdisplayed in a textbox. My problem is when I try to instantiate Items, it spits out the error message: Unable to get value of the property 'Items': object is null or undefined. This also affects my add and remove operations.

UPDATE

When I do alert(JSON.stringify(this.MyModel));, it shows that MyModel is undefined, but when I do alert(JSON.stringify(@Html.Raw(initialData))); my model is displayed in JSON format. So, my Model is serializing correctly, but knockout is unable to create an observable property from a C# variable? I don't know. Razor is a pain.

Mr Jones · Accepted Answer · 2012-08-30 15:46:33Z

5

The ViewModel should be constructed as follows:

@{
    var initialData = new JavaScriptSerializer().Serialize(Model);
}
var data = @Html.Raw(initialData);
function ViewModel(data) {
    var self = this;
    self.Name = ko.observable(data.Name);
    self.Items = ko.observableArray(data.Items);
    self.addItem = function() { self.Items.push(""); };
    self.removeItem = function(data) { self.Items.remove(data); }
}
$(document).ready(function() {ko.applyBindings(new ViewModel(data)); });

answered Aug 30, 2012 at 15:46

Mr Jones

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Comments

NibblyPig · Accepted Answer · 2012-08-29 15:46:08Z

2

I think that initialData is a C# variable but you're trying to alert it through javascript.

It's a bit confusing because it's hard to tell how razor is treating the var within the @{ }

If you want to stringify it you'll have to put it into a javascript variable first. Something like:

var jsInitialData = @{Html.Raw(initialData)}

Razor is a bit of a pain within javascript blocks so that won't work exactly, but I suspect you need something along those lines.

answered Aug 29, 2012 at 15:46

NibblyPig

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3 Comments

Mr Jones Over a year ago

I should've realized that. So, my model is being serialized correctly, but that still doesn't explain why I can't instantiate Items. Am i using the wrong syntax?

NibblyPig Over a year ago

How are you trying to instantiate it?

Mr Jones Over a year ago

Items: ko.observableArray(this.MyModel.Items)

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