getting the ng-object selected with ng-change

you also coud try this:

<select  ng-model="selectedItem" ng-change="update()">
   <option ng-repeat="item in items" 
         ng-selected="selectedItem == item.Id" value="{{item.Id}}">
      {{item.Name}}
   </option>
</select>

You can also directly get selected value using following code

 <select ng-options='t.name for t in templates'
                  ng-change='selectedTemplate(t.url)'></select>

script.js

 $scope.selectedTemplate = function(pTemplate) {
    //Your logic
    alert('Template Url is : '+pTemplate);
}

If Divyesh Rupawala's answer doesn't work (passing the current item as the parameter), then please see the onChanged() function in this Plunker. It's using this:

http://plnkr.co/edit/B5TDQJ

Instead of setting the ng-model to item.size.code, how about setting it to size:

<select ng-options="size as size.name for size in sizes" 
   ng-model="item" ng-change="update()"></select>

Then in your update() method, $scope.item will be set to the currently selected item.

And whatever code needed item.size.code, can get that property via $scope.item.code.

Fiddle.

Update based on more info in comments:

Use some other $scope property for your select ng-model then:

<select ng-options="size as size.name for size in sizes" 
   ng-model="selectedItem" ng-change="update()"></select>

Controller:

$scope.update = function() {
   $scope.item.size.code = $scope.selectedItem.code
   // use $scope.selectedItem.code and $scope.selectedItem.name here
   // for other stuff ...
}