Knockoutjs mapping and unstructured data

Question

How to use unstructured data with knockoutjs mapping plugin? For example source json:

[
    {
        "id": 1,
        "name": "Store #1",
        "address": "City #1"
    },
    {
        "id": 2,
        "name": "Store #2"
    }
]

Store #2 without address. My template:

<ul data-bind='foreach: data'>
    <li data-bind='with: id'>
        <a href data-bind='text: name, click: function () { $parent.view($data, $index()) }'>           
        </a>
        <span data-bind='text: address'></span> 
   </li>
</ul>

My viewModel

Module.store = function () {

    var self = this;

    self.data = ko.mapping.fromJS([]);
    self.init = function () {
        $.getJSON('json/stores.json', function (stores) {
            ko.mapping.fromJS(stores, self.data);
        });
    };
};

If I run this code, I get error:

Uncaught ReferenceError: Unable to process binding "text: function (){return address }" Message: address is not defined

For Store #2

How can I set null or empty string for Store #2 address property?

Answer 1

If your view shows the address, then your viewmodel must contain that property.

Make a viewmodel for the individual stores:

Module.Store = function (data) {
    this.id = null;
    this.name = null;
    this.address = null;

    ko.mapping.fromJS(data, {}, this);
}

and a use mapping definition (see documentation) in your store list:

Module.StoreList = function () {
    var self = this,
        mappingDefinition = {
            create: function (options) {
                return new Module.Store(options.data);
            }
        };

    self.stores = ko.observableArray();

    self.viewStore = function (store) {
        // ...
    };
    self.init = function () {
        $.getJSON('json/stores.json', function (stores) {
            ko.mapping.fromJS(stores, mappingDefinition, self.stores);
        });
    };
};

Modified view (as a general rule, try to avoid inline functions in the view definition):

<ul data-bind='foreach: stores'>
    <li>
        <a href data-bind='text: name, click: $parent.viewStore'></a>
        <span data-bind='text: address'></span> 
    </li>
</ul>

Answer 2

It doesn't seems to me that knockout-mapping-plugin has that functionality out of the box. Probably you should consider to try another workaround for that issue, I can see at least two:

1) returning json with null from server

2) displaying that span conditionally like:

<ul data-bind='foreach: data'>
    <li data-bind='with: id'>
        <a href data-bind='text: name, click: function () { $parent.view($data, $index()) }'>           
        </a>
        <!-- ko if: address -->
        <span data-bind='text: address'></span> 
        <!-- /ko -->
   </li>
</ul>