angularjs save changes after digest has finished - angularjs

Question

I think this might be quite common use-case with any angular app. I am simply watching some objects on my scope that are changed as part of several digest cycles. After digesting them (changing their values via databinding) has finished, I want to save them to databse.
A. Now, with the current solutions I see following problems:
running save in $timeout() - how to assure that save is called only
once
running a custom function in $scope.$evalAsync - how to find out what has been chaged
There are of course solutions to both of these prolblems, but non of those I know seem ehough elegant to me.
The question is: What is the most elegant solution to the problem?
B. In particular, what are the best practices to
make sure that save gets called only once in a digest cycle
find out that object is dirty after last digest

Answer 1

Here is a solution I've found working best for me - as an AMD modul. Inspired by Underscore.
/**
* Service function that helps to avoid multiple calls
* of a function (typically save()) during angular digest process.
* $apply will be called after original function returns;
*/
define(['app'], function (app) {
app.factory('debounce', ['$timeout', function ($timeout) {
return function(fn){ // debounce fn
var nthCall = 0;
return function(){ // intercepting fn
var that = this;
var argz = arguments;
nthCall++;
var later = (function(version){
return function(){
if (version === nthCall){
return fn.apply(that, argz);
}
};
})(nthCall);
return $timeout(later,0, true);
};
};
}]);
});
/*************************/
//Use it like this:
$scope.$watch('order', function(newOrder){
$scope.orderRules.apply(newOrder); // changing properties on order
}, true);
$scope.$watch('order.valid', function(newOrder){
$scope.save(newOrder); //will be called multiple times while digested by angular
});
$scope.save = debounce(function(order){
// POST your order here ...$http....
// debounce() will make sure save() will be called only once
});