Having difficulty grasping the concept of AngularJS Promises

As I deepen my understanding of AngularJS, I find myself faced with the challenge of adapting code examples to fit my own projects.

In this particular example sourced from Urish, it is clear that the variable "promise" must encompass the necessary functions and queries for the function to progress smoothly.

var promise = asyncFunction(parameters); 

promise.then( 
function (result) { 
 // Perform actions based on result data 
}, 
function (error) { 
 // Handle errors or exceptions 
}); 

In my scenario, where I intend to execute two $http queries initially and then utilize the retrieved data to populate the URL for a third query, would the code structure be similar to the following snippet?

var promise = $scope.getDetails(id); 

  $scope.getDetails = function (id) {
    $http.get('http://api.discogs.com/artists/' + id).
      success(function(data) {
          $scope.artist = data;
      });
    $http.get('http://api.discogs.com/artists/' + id + '/releases?page=1&per_page=100').
      success(function(data2) {
          $scope.releases = data2.releases;
      });
    $scope.clicked = true;
    $scope.sliding = true;
  } 

  promise.then( 
    $scope.getImages = function (title, name) {
        $http.get('http://ws.audioscrobbler.com/2.0/?method=album.getinfo&api_key=e8aefa857fc74255570c1ee62b01cdba&artist=' + name + '&album='+ title +'&format=json').
          success(function(data4) {
              $scope.images = data4;
          });
    },
  function (error) { 
   // Handle error (exception, etc). 
  }); 

Does this implementation align with best practices? Are there any crucial elements missing from this approach?

UPDATE: I've set up a functional Plunker based on Benjamin's solution, but it seems to encounter issues with AngularJS integration. Any insights on where the problem may lie?

Answer №1

If you want to merge promises together, as Florian recommended, you can use the .all method:

$scope.getDetails = function (id) {
    var api = 'http://api.discogs.com/artists/';
    return $q.all([$http.get(api + id),
                  $http.get(api + id + '/releases?page=1&per_page=100')]);
});

Here is how you would use it:

$scope.getDetails(YOURID).then(function(results){
    $scope.artist = results[0];
    $scope.releases = results[1].releases;
});

If you have three queries:

$scope.getDetails(YOURID).then(function(results){
    $scope.artist = results[0];
    $scope.releases = results[1].releases;
    // data for getImages available here
    return $http.get('http://ws.audioscrobbler.com/2.0/?...' + results[0]...
});

(Also, I recommend putting this logic in a service)

Answer №2

  $scope.viewArtistDetails = function (artistId) {
    $scope.showDetails = true;
    $scope.slideIn = true;
return $q.all(    $http.get('http://api.artshop.com/artists/' + artistId).
      success(function(artistData) {
          $scope.currentArtist = artistData;
      }),
    $http.get('http://api.artshop.com/artists/' + artistId + '/albums?page=1&per_page=100').
      success(function(albumData) {
          $scope.albums = albumData.list;
      }));
}

This controller requires $q as a dependency. $q.all() is used to handle multiple promises and returns a promise that will resolve or reject based on the individual promises passed in. Learn more about $q at http://docs.angularjs.org/api/ng/service/$q You can use

var detailsPromise = $scope.viewArtistDetails(artistId);
detailsPromise.then(...,...);

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