Conditionally apply hasDropdown directive on ng-repeated element - angularjs

Question

I'm working on a project where I use both angularJS and foundation, so I'm making use of the Angular Foundation project to get all the javascript parts of foundation working. I just upgraded from 0.2.2 to 0.3.1, causing a problem in the top bar directive.
Before, I could use a class has-dropdown to indicate a "top-bar" menu item that has a dropdown in it. Since the menu items are taken from a list and only some have an actual dropdown, I would use the following code:
<li ng-repeat="item in ctrl.items" class="{{item.subItems.length > 0 ? 'has-dropdown' : ''}}">
However, the latest version requires an attribute of has-dropdown instead of the class. I tried several solutions to include this attribute conditionally, but none seem to work:
<li ng-repeat="item in ctrl.items" has-dropdown="{{item.subItems.length > 0}}">
This gives me a true or false value, but in both cases the directive is actually active. Same goes for using ng-attr-has-dropdown.
this answer uses a method of conditionally applying one or the other element, one with and one without the directive attribute. That doesn't work if the same element is the one holding the ng-repeat so i can't think of any way to make that work for my code example.
this answer I do not understand. Is this applicable to me? If so, roughly how would this work? Due to the setup of the project I've written a couple of controllers and services so far but I have hardly any experience with custom directives so far.
So in short, is this possible, and how?

Answer 1

As per this answer, from Angular>=1.3 you can use ngAttr to achieve this (docs):
If any expression in the interpolated string results in undefined, the
attribute is removed and not added to the element.
So, for example:
<li ng-repeat="item in ctrl.items" ng-attr-has-dropdown="{{ item.subItems.length > 0 ? true : undefined }}">
angular.module('app', []).controller('testCtrl', ['$scope',
function ($scope) {
$scope.ctrl = {
items: [{
subItems: [1,2,3,4], name: 'Item 1'
},{
subItems: [], name: 'Item 2'
},{
subItems: [1,2,3,4], name: 'Item 3'
}]
};
}
]);
<div ng-app="app">
<ul ng-controller="testCtrl">
<li ng-repeat="item in ctrl.items" ng-attr-has-dropdown="{{ item.subItems.length > 0 ? true : undefined }}">
{{item.name}}
</li>
</ul>
</div>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.14/angular.min.js"></script>

Answer 2

Ok, I made a directive. All <li> will need an initial attr of:
is-drop-down="{{item.subItems.length > 0}}"
Then the directive checks that value and for somereason its returning true as a string. Perhaps some onc can shed some light on that
app.directive('isDropDown', function () {
return {
link: function (scope, el, attrs) {
if (attrs.isDropDown == 'true')
{
return el.attr('has-dropdown', true); //true or whatever this value needs to be
}
}
};
});
http://jsfiddle.net/1qyxrcd3/
If you inspect test2 you will see it has a has-dropdown attribute. There is probably a cleaner solution, but this is all I know. I'm still new to angular.
edit I noticed a couple extra commas in my example json data..take note, still works, but they shouldn't be there.