title: How to wait for $firebaseArray data
body: <p>Below is my firebase query that works fine:</p>
  
  <pre><code>var orderedPlayers = databaseService.players.orderByChild("id");
  </code></pre>
  
  <p>My intention is to then have the point total of each player to be added together:</p>
  
  <pre><code>            $scope.sum = function(items, prop){
              return items.reduce( function(a, b){
              return a + b[prop];
              }, 0);
              };
  
              $scope.selectedPlayers = $firebaseArray (orderedPlayers);
              $scope.totalGoals = $scope.sum($scope.players, 'goals');
  </code></pre>
  
  <p>The issue is that when i change the number of goals directly in the firebase database, there is a real time updating of the goals under each player as displayed in my scope but there is no corresponding change in the resulting total number of goals. </p>
  
  <p>i.e. <code>$scope.selectedPlayers updates in real time</code> but <code>$scope.totalGoals</code> only updates after refreshing the page. </p>
  
  <p>Is it possible to have the latter update in realtime as well? </p>