Question

I am trying to use the value binding on the select element, as described in this fiddle: http://jsfiddle.net/MikeEast/nM6dd/2/

However, I cannot seem to be able to set the selected option (value binding).

I know I can use the optionsValue binding, but that makes the value a string instead of an object which is not preferable. If that is the only way to go, how would I do to ensure that the selected option is written back to the view model?

Thanks!

Answer 1

Here is the solution. You have to add the attribute optionsValue: 'id' to the data-bind.
You also have to put a function in you viewModel that returns the selected object.

var viewModel = function() {
  this.items = ko.observableArray([
    { id: 1, name: "Apple" }, 
    { id: 2, name: "Orange"},
    { id: 3, name: "Banana"}
  ]);
  this.selectedItemId = ko.observable(3);
  this.selectedItem = function() {
    var self = this;
    return ko.utils.arrayFirst(this.items(), function(item) {
      return self.selectedItemId() == item.id;
    });
  }.bind(this);
};

var vm = new viewModel();
ko.applyBindings(vm);

<script src="https://cdnjs.cloudflare.com/ajax/libs/knockout/1.2.1/knockout-min.js"></script>
<select data-bind="options: items, optionsText: 'name', optionsValue: 'id', value: selectedItemId"></select>
<span data-bind="text: selectedItem().name"></span>

Cheers!