AngularJS: Using Shared Service(with $resource) to share data between controllers, but how to define callback functions?

Question

AngularJS: Using Shared Service(with $resource) to share data between controllers, but how to define callback functions?

Note: I also posted this question on the AngularJS mailing list here: https://groups.google.com/forum/#!topic/angular/UC8_pZsdn2U

Hi All,

I'm building my first AngularJS app and am not very familiar with Javascript to begin with so any guidance will be much appreciated :)

My App has two controllers, ClientController and CountryController. In CountryController, I'm retrieving a list of countries from a CountryService that uses the $resource object. This works fine, but I want to be able to share the list of countries with the ClientController. After some research, I read that I should use the CountryService to store the data and inject that service into both controllers.

This was the code I had before:

CountryService:

services.factory('CountryService', function($resource) {
    return $resource('http://localhost:port/restwrapper/client.json', {port: ':8080'});
});

CountryController:

//Get list of countries         
//inherently async query using deferred promise
$scope.countries = CountryService.query(function(result){       
        //preselected first entry as default
    $scope.selected.country = $scope.countries[0];  
});

And after my changes, they look like this:

CountryService:

services.factory('CountryService', function($resource) {
    var countryService = {};

    var data;
    var resource = $resource('http://localhost:port/restwrapper/country.json', {port: ':8080'});

    var countries = function() {
        data = resource.query();
        return data;
    }

    return {
        getCountries: function() {
            if(data) {
                console.log("returning cached data");
                return data;
            } else {
                console.log("getting countries from server");
                return countries(); 
            }

        }
    };
  });

CountryController:

$scope.countries = CountryService.getCountries(function(result){
        console.log("i need a callback function here...");
});

The problem is that I used to be able to use the callback function in $resource.query() to preselect a default selection, but now that I've moved the query() call to within my CountryService, I seemed to have lost what.

What's the best way to go about solving this problem?

Thanks for your help, Shaun

javascript
angularjs

Answer 1

Ok..so looks like I solved the problem by passing a callback function all the way up to the resource.query() call. Still not sure if this is the best way to do this.

For reference, this is what I did:

CountryController:

$scope.countries = CountryService.getCountries(function(){
    //preselected default
    $scope.selected.country = $scope.countries[0];  
});

CountryService:

//Country Service. Will contain all relevant rest methods here
services.factory('CountryService', function($resource) {
    var countryService = {};

    var data;
    var resource = $resource('http://localhost:port/restwrapper/country.json', {port: ':8080'});

    var countries = function(callback) {
        data = resource.query(callback);
        return data;
    }


    return {
        getCountries: function(callback) {
            if(data) {
                console.log("returning cached data");
                return data;
            } else {
                console.log("getting countries from server");
                return countries(callback); 
            }

        }
    };
  });

Answer 2

You should take a look at the $q service, you can do:

promise.then(callback);

From 1.1.3, you can access promises with $then, for exemple resource.query().$then(callback);

Answer 3

In this new scenario you could use a $scope.$watch. The way you use it is as follows.

$scope.countries = CountryService.getCountries();

$scope.$watch('countries',function(newValue){
//need to check if newValue has a value because 
//the first time watch fires it will be undefined.
    if(newValue && newValue.length > 0 ){
        $scope.selected.country = $scope.countries[0];
    }
});

Hope this helps.

Answer 4

AngularJS has its own way of caching queries, which you should use. As for the callback, it's no use assigning the query to a variable, since a promise will be returned anyway. You should simply always expect a promise, and pass your callback inside success or finally.