Directive trigger controller before model is updated - angularjs

Question

I created a custom directive that create two buttons. Each button use ng-click to call a method inside the directive to change a value of the model and then call the controller to update the value in the database. In this way the controller is called before the model is updated because it always use the old value.
If I apply inside the directive $scope.$apply() everything works fine, except an error is fired in the consolle because there are an $apply() executing yet. How properly wait the model update before to call the controller?
The directive is used into an ng-repeat that iterate an array.
Logic I used is:
User Click one of the Buttons of the switch (On or Off i.e.)
Button Trigger directive setModel(value) method
setModel(value) set value to the model and call controller passing index of the object
controller get the object by index and update in database
If i try to send the value edited to the controller, of course, it works, but i would play with models and not with each values. Why the model is updated before controller do it's $http calls?
This is the directive:
app.directive('ngSwitch', function () {
return {
scope: {
model: '=ngSwitch',
index: '=index', //Index in the array
switchValue1: '#switchValue1',
switchDesc1: '#switchDesc1',
switchValue2: '#switchValue2',
switchDesc2: '#switchDesc2',
callback: '=callback'
},
link: function (scope, elm, attr) {
scope.saving = false;
scope.setModel = function (value) {
scope.model = value == 1 ? scope.switchValue1 : scope.switchValue2;
scope.saving = true;
scope.$apply();//IF I DON'T USE $apply, IT DOESN'T WORK
scope.callback(scope.index)
}
},
templateUrl: 'components/direttive/ngSwitch.html'
};
});