AngularJS $http vs service vs ngResource

Question

I would like to understand the advantages and disadvantages of using a simple $http request to a server and/or wrapping that request in a service versus using a ngResource object (other than the obvious regarding a RESTful resource).

From my understanding the $http requests are low level but very flexible and configurable whereas when dealing with a RESTful API the ngResource objects make communication very simple.

I guess what I am enquiring about is given a very simple scenario, say retrieval of data from a server (GET request of array of objects say) is it more efficient to simply use a $http request as opposed to either wrapping it in a service (should this always be the case?) or using an ngResource object?

Any thoughts here would be appreciated. For example, a $http response can be cached, but can an ngResource?

Answer 1

Decided I'll formulate this into an answer since in the comments we worked out basically what you wanted to know:

Using $http or $resource the results can still be cached, you pointed out the reasons to use one over the other really in your question. If you have a RESTful interface then using $resource is better since you'll end up writing less boiler-plate code that is common to a RESTful interface, if you're not using a RESTful service then $http makes more sense. You can cache data either way http://www.pseudobry.com/power-up-http-with-caching/

I think putting $http or $resource requests into a service just generally works out better because you want to have access to the data from multiple locations and the service acts as a singleton. So, basically you can handle any kind of caching you want to do there and controllers can all just watch the appropriate services to update their own data. I've found that a combo of $watch in the controllers for data on the service and returning the promises from my service's methods gives me the most flexibility with how to update things in the controller.

I'd put something like this in my controller having the exampleService injected at the top of the controller definition.

angular.module("exampleApp", []).service('exampleService', ["$http", "$q" ,function ($http, $q) {
    var service = {
        returnedData: [],
        dataLoaded:{},
        getData = function(forceRefresh)
        {
            var deferred = $q.defer();

            if(!service.dataLoaded.genericData || forceRefresh)
            {
                $http.get("php/getSomeData.php").success(function(data){
                    //service.returnedData = data;
                    //As Mark mentions in the comments below the line above could be replaced by
                    angular.copy(data, service.returnedData);
                    //if the intention of the watch is just to update the data
                    //in which case the watch is unnecessary and data can
                    //be passed directly from the service to the controller
                    service.dataLoaded.genericData = true;
                    deferred.resolve(service.returnedData);
                });
            }
            else
            {
                deferred.resolve(service.returnedData);
            }

            return deferred.promise;
        },
        addSomeData:function(someDataToAdd)
        {
            $http.post("php/addSomeData.php", someDataToAdd).success(function(data){
                service.getData(true);
            });
        }
    };
    service.getData();
    return service;
}]).controller("ExampleCtrl", ["$scope", "exampleService", function($scope, exampleService){
  //$scope.$watch(function() {return exampleService.returnedData}, function(returnedData){
  //  $scope.myModel.someData = returnedData;
  //});
  //if not using angular.copy() in service just use watch above
  $scope.myModel.someData = exampleService.returnedData;
}]);

Also here's a nice video from the Angular team on Best Practices that I'm still re-watching and slowly absorbing over time.

http://www.youtube.com/watch?v=ZhfUv0spHCY

Specifically on services vs controllers: http://www.youtube.com/watch?v=ZhfUv0spHCY&t=26m41s

Answer 2

There is one far more meaningful difference than whether they can be cached or not.

Using a resource will remove the need to set up $watches on the service or the returned data. You will not have to work with promises at all either. Essentially, it eliminates the need to do any of what shaunhusain is doing above in his example.

A call to a resource method returns an empty instance of the structure associated with that resource, and you can and should bind to it directly. This same instance will fill with data at some later time. Since you have bound to the instance, when it fills in, your display will update automatically.

Resources can also provide an encapsulated means of transforming requests and responses of the services it provides, making it all invisible to the client of the resource.

Resources are like services on steroids.