在Ionic1和Angularfire中，我如何检索一个子数组？

angular.module('app.controllers', ['firebase'])

var ref = new Firebase('https://your-firebase-url.firebaseio.com/');

{
  "users": {
    "user1": {
      "name": "John",
      "items": [
        "item1",
        "item2",
        "item3"
      ]
    },
    "user2": {
      "name": "Jane",
      "items": [
        "item4",
        "item5",
        "item6"
      ]
    }
  }
}

var userRef = ref.child('users/user1');
var itemsArray = $firebaseArray(userRef.child('items'));

itemsArray.$loaded().then(function() {
  console.log(itemsArray); // 子数组已检索到
});