Add Proper Support For Non-Singleton Services

[Undistraction]

Currently, there are two ways to do this:

1. By returning some sort of Provider from Service::factory. This then leaves the dependent class to create an instance using provider.getInstance() or similar.
2. By returning a constructor. This then leaves the dependent class to create an instance using new ServiceClass()

Both mean that the dependent class has to know that the service is non-singleton and know how to generate/create a new instance. A dependent object shouldn't know or care whether a service it depends on is a Singleton or one of many instances. This is something that should be declarable on the Service / when the service is defined.

[kstep]

Could you give an example code to illustrate your point? I feel like there's no much of an issue in here, just a misuse of services, but I may be wrong.

[petebacondarwin]

I agree with @kstep.

All services are singletons. The only things that can be injected that are not singletons are controllers.

There is a pattern for creating new instances if that is what you want: Simply make the service a function that returns new instances each time you call the function. This is how $resource works:

someModule.factory('getMyNonSingletonObject', function(injectables) {
  return function() {
    // create and return your non singleton object here e.g.
    return new SomeObject();
  };
});

This can be use as:

var instance1 = getMyNonSingletonObject();
var instance2 = getMyNonSingletonObject();

expect(instance1).not.toBe(instance2);

[Undistraction]

All services are singletons. The only things that can be injected that are not singletons are controllers.

I know that they are at the moment.

There is a pattern for creating new instances if that is what you want: Simply make the service a function that r       returns new instances each time you call the function. This is how $resource works:

Yes. I mention this in my ticket under 2. It means that the dependent class has to treat the service differently. It would be nicer if the dependent didn't know or care whether the service was a Singleton or not. At the moment, non-singleton services feel like a hack.

Why has the decision been made that Services must be Singletons? It seems pretty commonplace for people to store state on Services, so why enforce their Singletoness? Why not allow for multiple instances of the same Service?

[MikeMcElroy]

If you want to store state on a Service to be accessed in another controller, then don't you want Singleton-ness? Otherwise you're wiring up a lot of interdependencies. (i.e. inject this instance of UserService to these controllers, and this instance of UserService to these other controllers)

This would be a lot easier to understand if you had some code to show the actual need.

[kstep]

Actually you can get another instance of any service by creating new injector. But theirs no much in it usually. I still think you misunderstand services system in AngularJS.

[Youkai-no-nii-chan]

I whant to use MVVM in my project and i need services to be injected in my ViewModels.
For example :

someModule.factory('ItemViewModel', function($http) {
  return function() {
    // For each item in list there should ne instance of ItemViewModel
    return new ItemViewModel($http);
  };
});

// I create ViewModels like this 
var $injector.get('ItemViewModel');
viewModel.data = someData;
// And of course it is created as singleton and doesn't works as intended

It whould be great if i could easily create ViewModels wihtout creating separate factorу for each ViewModel type.

[kstep]

Isn't it better this way?

someModule.factory('ItemViewModel', function($http) {
  return function() {
    // For each item in list there should ne instance of ItemViewModel
    return function (data) {
      var model = new ItemViewModel($http);
      model.data = data;
      return data;
    };
  };
});

var vmFactory = $injector.get('ItemViewModel');
var viewModel = vmFactory(data);

Especially if you inject your factory the usual way:

someModule.controller('MyCtrl', function (ItemViewModel, $scope) {
  $scope.model = ItemViewModel(data);
});

[Youkai-no-nii-chan]

Yeah... maybe it's better way to do it.