knockout cascading dropdown

Question

I have two dropdowns one depending on other (cascading). The selection on the ‘MainCategories’ decides the items for ‘SubCategories’. Also, the selection on the ‘MainCategories’ decides the visibility of a table row as well. The following is what I tried:

<table>
    <tbody data-bind="foreach: contacts">
        <tr>
            <td>MainCategories:
                <select data-bind='options: MyCategories, value: mycategory, optionsText: "Type", optionsValue: "Type",optionsCaption: "Select..."'></select>
            </td>
            <td>
                <!-- ko with: mycategory -->SubCategories:
                <select data-bind='options: Categories, optionsText: "Category", optionsCaption: "Select...", value: $parent.product'></select>
                <!-- /ko -->
            </td>
        </tr>
        <tr data-bind="visible:mycategory()=='Type1'">
            <td>I am visible</td>
        </tr>
    </tbody>
</table>

<script type = "text/javascript" >
    var MyCategories = [{
        "Categories": [{
            "Category": "Category1"
        }, {
            "Category": "Category2"
        }],
        "Type": "Type1"
    }, {
        "Categories": [{
            "Category": "Category3"
        }, {
            "Category": "Category4"
        }],
        "Type": "Type2"
    }];
    var initialData = [{
        category: "Mobile",
        product: "Nokia"
    }];

    var ContactsModel = function (contacts) {
        var self = this;
        self.contacts = ko.observableArray(ko.utils.arrayMap(contacts, function (contact) {
            return {
                mycategory: ko.observable(contact.category),
                product: ko.observable(contact.product)
            };
        }));

    };

    ko.applyBindings(new ContactsModel(initialData));
</script>

If I remove optionsValue: "Type", then the ‘SubCategories’ gets the right items. But the visibility of the table row is not working as expected. If I have optionsValue: "Type", then the ‘SubCategories’ is not getting populated. And also, when I change the options of ‘MainCategories’ 1 or 2 times, then only the visibility is working fine.

Please help me find what I am doing wrong here. Thanks,

Answer 1

I read your question and I have a feeling that this will answer it if not address it enough that you can apply it -

*Problem * -

You need to have a cascading dropdown using Knockout to select a value and set your observable equal to the child select's selected object.

*Solution * -

Use a computed to make the second dropdown dependent on the first. Example -

var selectedParent = ko.observable();

var parentCategories = ko.observableArray(MyCategories);

var childCategories = ko.computed(function () {
    if (!selectedParent()) { return new Array(); }
    var childArray = [];
    // get the values you want for the child here
    return childArray;
});

By adding if (!selectedParent()) you are making the childCategories dependent on the selectedParent. Whenever the selection changes the childCategories will automatically update.

Then your view can be something like this -

<td>MainCategories:
                <select data-bind='options: parentCategories, value: selectedParent, optionsText: "Type", optionsValue: "Type",optionsCaption: "Select..."'></select>
            </td>
            <td> SubCategories:
                <select data-bind='options: childCategories, optionsText: "Category", optionsCaption: "Select...", value: $parent.product'></select>
                <!-- /ko -->
            </td>