$scope.$apply making dropdown act weird - angularjs

Question

I have a dropdown;
<select class="form-control" data-ng-model="selected_category" data-ng-change="search(true, true)">
<option value="0">Select Category</option>
<option value="{{category.id}}" data-ng-repeat="category in categories">{{category.name}}</option>
</select>
Which works perfect. However, I am manipulating the scope outside of Angular (valid reason) and I use this (It's in coffeescript but easy to understand)
scope.$apply (s) ->
s.units = _me.attr('data-units')
s.selected_category = parseInt(_me.attr('data-category'))
s.search(true,true)
It appears to work in that everything depending on that $scope.selected_category variable changes (The correct products / text comes up) but the dropdown just goes blank if I've selected Select Category (IE: Not changed it since that change) and stays the same if anything else is selected. Looking at the blank dropdown when I use the element inspector in chrome I can see this:
<option value="? number:31 ?"></option>
What's up with that?

Answer 1

It appears that you are missing the ng-selected attribute on option to let Angular know which option is currently selected:
<select class="form-control" data-ng-model="selected_category" data-ng-change="search(true, true)">
<option value="0">Select Category</option>
<option value="{{category.id}}" data-ng-selected="selected_category.id == category.id" data-ng-repeat="category in categories">{{category.name}}</option>
</select>
However, it is prefered to use ng-options if you don't need to do anything to advanced. So, I'd recommend (as #TheSharpieOne mentions in comments), that you change to this:
<select ng-model="selected_category" ng-options="c.name for c in categories">
<option value="">Select Category</option>
</select>
If you need to track by the id then use a track by clause:
<select ng-model="selected_category" ng-options="c.name for c in categories track by c.id">
<option value="">Select Category</option>
</select>