Concern
I am facing challenges with AngularJS promise synchronization and sequencing as my app expands across multiple controllers and services. In this scenario, I have an articles controller named ArticleController along with a related service named ArticleDataService. The process involves:
- Fetching articles from a server,
- Selecting the first article from the list, and
- Retrieving the related images using the current article (
currentArticle).
Issue
The data retrieval from the server typically takes around 1 second to fetch the article records and images. However, during this latency period, the second controller (ImagesController) searches for cached data in the ImageDataService module but does not find it due to unresolved promises from the Article Controller resulting from server delays. As a result, the ArticleController has not yet cached the images data, leading to errors in subsequent image-related code execution. Attempting to return $q.when(cachedImages) on cachedImages results in an unresolved promise due to separate $q resolve sequences in both controllers without a centralized approach to manage sequencing.
Resolution Attempts
- Using $rootScope Watch Events: While events within services or controller watches can be used, this method seems to introduce overhead, debugging challenges, and potential testing issues given the intricate nested structure inside the
ImageDataService.
Approach Experimentation
Example: Implementing the following snippet in the second controller ImagesController demonstrated functionality in synchronizing data access while maintaining time management for dependent directives such as chart data visualization.
var articleModelListener = $scope.$watch(function () {
return ImageDataService.getImages();
},
function (newValue, oldValue) {
if (newValue !== undefined && newValue !== null) {
if (Object.keys(newValue).length > 0) {
iCtrl.dataUrls = newValue;
// Terminate $watcher
articleModelListener();
}
}
});
- Timeout Approach: Wrapping all relevant code with timeouts proved challenging as it led to performance degradation requiring additional handling in other controllers like Chart and Poll controllers.
- Data Resolution via Central Service Provider: Centralizing data resolution efforts in an uber DataService resolved sequencing dilemmas but introduced new synchronization requirements across controllers.
Inquiry and Assumption
Considering timeout wrapping and interval usage as potentially detrimental waterfall practices, would sticking with promises or exploring event-based approaches involving $rootScope watches and controller scoping offers a more viable solution?
Problem Code Illustration Below:
PLEASE NOTE:
1. To maintain brevity, specific code excerpts are omitted for illustration purposes.
2. Your input and guidance are greatly appreciated. Apologies for any terminology misuse.
HTML Markup
<section ng-controller="MainController as mCtrl">
// Specific HTML elements excluded for brevity
</section>
<section ng-controller="ImagesController as iCtrl">
// Specific HTML elements excluded for brevity
</section>
Angular JS Version (1.4.*)
<pre><code>
angular.module('articles', [
])
.controller('ArticlesController', ['ArticleDataServices', 'ImageDataService', function(ArticleDataServices, ImageDataService) {
var mCtrl = this;
// Controller logic for retrieving and caching article data
}])
</code></pre>
Note: In the ImagesController, issues arise when executing methods ahead of the first controller awaiting server responses, culminating in unmet promises inhibiting data returns.
<pre><code>
.controller('ImagesController', ['ImageDataService', function(ImageDataService) {
// Images Controller logic
}])
.service('ArticleDataServices', ['$http',', $q', function($http, $q){
// Article Data Service logic
}])
.service('ImageDataService',['$http',', $q', function($http, $q){
// Image Data Service logic
}]);
</code></pre>