title: Creating and adding to arrays in angularFire / Firebase
body: <p>I am trying to build an app with angularjs and Firebase similar to a forum for helping my classmates with problems. I also want people to be able to 'reply' to the specific problems the classmates are having, so I create an object with many values in the angularjs factory, like this:</p>
  
  <pre><code>factory.addError = function() {
   factory.errors.$add({
    ...
    replies: []
   });
  };
  </code></pre>
  
  <p>The problem with this is that Firebase doesn't save parameters with empty values for placeholders, such as the parameter 'replies' above. I have tried to hard code a placeholder value into the array, but that seems like a very patchy solution, and that comes with it's own set of problems for me having to delete out  the data in Firebase. For reference, here is the code in the linked controller:</p>
  
  <pre><code>$scope.error.replies.$push({
    name: $scope.replyName,
    message: $scope.replyMessage,
    time: (new Date()).toString(),
    upvote: 0
  });
  </code></pre>
  
  <p>How do you initialize an empty array into the object? And will $push properly use Firebase's commands to save it to it's own set of data?</p>