Attempting to retrieve data from ref.on() method within a factory and pass it to a controller

Question

Attempting to retrieve data from ref.on() method within a factory and pass it to a controller

Having trouble extracting the value from a Firebase query in my factory to the controller. Any suggestions or ideas would be greatly appreciated!

Controller:

main.controller("mainCtrl", function($scope, totalusers){
  $scope.city = "whatever";
  $scope.total = totalusers.getusers($scope.city);
});

Factory (contains the query to retrieve the number of users with the specified Name):

app.factory("totalusers", function(FURL) {
    var gettotalusers      = {};
    gettotalusers.getusers = function(city) {
        var tusers = new Firebase(FURL + "/Users/" + city);
        var count  = 0;

        tusers.on("value", function(snapshot) {
            snapshot.forEach(function(child) {
                if (child.val().Name != undefined) {
                    count++;
                }
            });
            var total = count;
            return total;
        });

    }
    return gettotalusers;
});

If you have any insights or suggestions, feel free to share. Thanks in advance! ;)

javascript angularjs firebase

Answer 1

Answer №1

To retrieve the firebase value asynchronously, ensure that the count value remains at 0 when assigned to the total, which is then promptly returned. Utilize the $q service to establish a promise and resolve it upon receiving the firebase callback.

app.factory("totalusers", function(FURL, $q){
  var gettotalusers = {};
  gettotalusers.getusers = function(city){
    var tusers = new Firebase(FURL + "/Users/" + city);
    var count = 0;
    var deferred = $q.defer();

    tusers.on("value", function(snapshot){
      snapshot.forEach(function(child) {
        if(child.val().Name != undefined){
          count++;
        }
      });
      deferred.resolve(count);
    });

    return deferred.promise;
  }
  return gettotalusers;
});

In your controller, refrain from directly assigning the result. Instead, implement it within a promise handler method like this:

main.controller("mainCtrl", function($scope, totalusers){
  $scope.city = "whatever";
  totalusers.getusers($scope.city).then(
    function(total) {
      $scope.total = total;
    },
    function(err) {
      // handle error
    }
  );
});

For further information, refer to the $q documentation and familiarize yourself with the concept of promises. https://docs.angularjs.org/api/ng/service/$q

You can also consider refining your count using a more functional approach with filter and reduce:

var total = snapshot
  .filter(function(item) { return child.val().Name !== undefined })
  .reduce(function(acc, curr) {
    return acc + curr;
  }
);

Answer 2

To retrieve the firebase value asynchronously, ensure that the count value remains at 0 when assigned to the total, which is then promptly returned. Utilize the $q service to establish a promise and resolve it upon receiving the firebase callback.

app.factory("totalusers", function(FURL, $q){
  var gettotalusers = {};
  gettotalusers.getusers = function(city){
    var tusers = new Firebase(FURL + "/Users/" + city);
    var count = 0;
    var deferred = $q.defer();

    tusers.on("value", function(snapshot){
      snapshot.forEach(function(child) {
        if(child.val().Name != undefined){
          count++;
        }
      });
      deferred.resolve(count);
    });

    return deferred.promise;
  }
  return gettotalusers;
});

In your controller, refrain from directly assigning the result. Instead, implement it within a promise handler method like this:

main.controller("mainCtrl", function($scope, totalusers){
  $scope.city = "whatever";
  totalusers.getusers($scope.city).then(
    function(total) {
      $scope.total = total;
    },
    function(err) {
      // handle error
    }
  );
});

For further information, refer to the $q documentation and familiarize yourself with the concept of promises. https://docs.angularjs.org/api/ng/service/$q

You can also consider refining your count using a more functional approach with filter and reduce:

var total = snapshot
  .filter(function(item) { return child.val().Name !== undefined })
  .reduce(function(acc, curr) {
    return acc + curr;
  }
);

Answer 3

Answer №2

Avoid using ref.on() in this particular situation as it can result in continuous synchronization of the node even after the function has completed its execution. It is recommended to utilize ref.off(), or better yet, opt for ref.once(). If you are working with the latest version of Firebase, this method returns a promise, eliminating the need for $q.

app.factory("totalusers", function(FURL) {
    var gettotalusers = {};

    gettotalusers.getusers = function(city) {
        var tusers = new Firebase(FURL + "/Users/" + city);

        return tusers.orderByChild("Name")
                     .startAt(false)
                     .once("value")
                     .then(function(snapshot) {
            return snapshot.numChildren();
        });
    };

    return gettotalusers;
});

Answer 4

Avoid using ref.on() in this particular situation as it can result in continuous synchronization of the node even after the function has completed its execution. It is recommended to utilize ref.off(), or better yet, opt for ref.once(). If you are working with the latest version of Firebase, this method returns a promise, eliminating the need for $q.

app.factory("totalusers", function(FURL) {
    var gettotalusers = {};

    gettotalusers.getusers = function(city) {
        var tusers = new Firebase(FURL + "/Users/" + city);

        return tusers.orderByChild("Name")
                     .startAt(false)
                     .once("value")
                     .then(function(snapshot) {
            return snapshot.numChildren();
        });
    };

    return gettotalusers;
});

Attempting to retrieve data from ref.on() method within a factory and pass it to a controller

Answer №1

Answer №2

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