AngularJS Service returning data instead of promise

Question

I have a question conserning the use of services or factories inside an AngularJS application.

I Want to write a service that will return data from an Api which i can use inside my controllers.

Lets say i want to have a call like $scope.people = myPeopleService.getPeople(); and inside my service want to check if i already have people and return those otherwise i want to do a $http.get() and fill the people inside my service and then return them. I do not want to have .then inside my controller. Is this even possible?

Answer 1

If you dont want to return the promise to the consumer of your service:

.service('...', function ($http) {
  var cachedResponse;

  this.getStuff = function () {
    if (cachedResponse) {
      return cachedResponse;
    }

    return $http.get('someUrl')
      .then(function (response) {
        cachedResponse = response;
        return response; // Return the response of your $http call. 
      });
  };
});

Answer 2

My solution is to return a reference to an object that might be empty at first, but will hold the data eventually:

app.factory('myPeopleService', function($http){

    var people = {};

    $http
        .post( "/api/PeopleService/getInitData", {
        }).success(function (data, status, headers, config) {
            angular.extend(people, data);
        }).error(function (data, status, headers, config) {
        });

    return {
        getPeople: function () {
            return people;
        }
    };
});

the key is to use angular.extend in order to preserve the object reference.

in the controller you can use ng-show until the data is fulfilled, and/or use watch for processing

Answer 3

You won't be able to escape that at some level, somewhere, this call is asynchronous. One part of your question is easy, caching data is just an option in the $http call:

$http.get(url, {cache: true})

If you expose this call from a service only one call will be made over the network, no changes are required in your controller code.

Another thing to look into is using your router's resolve feature (ui-router and the vanilla router both support resolve). This can clean up some of the code in your controller.

Answer 4

It is not possible to do it without a .then in your use case. Since you want to make use of $http to fetch the people and return them (if they were not present already). $http works asynchronously and would return a promise. Due to the asynchronous behavior of $http it becomes mandatory to handle the promise returned in the calling function.

Hope this helps!