有没有办法在Firebase子集合中编写模型列表

Question

我有一个模型，该模型包含其他模型的列表作为属性，我正在从用户填写的表单中动态收集该模型。 第一个模型的代码：

class Attraction {
  String atName;
  String atDiscreption;
  double latitude;
  double longitude;
  GeoPoint geoPoint;
  String atImageUrl;

  List<Timeline> timlines;

  Attraction(
      {
      this.atName,
      this.atDiscreption,
      this.geoPoint,
      this.latitude,
      this.longitude,
      this.atImageUrl,
      this.timlines});
} 

第二个模型的代码：

class Timeline {
  int date;
  String descreption;

  Timeline(this.date, this.descreption);
}

我正在使用此方法将第一个模型写到Firestore Firebase中：

final CollectionReference attractions =
      Firestore.instance.collection('attractions');

  Future updateAttractionData(Attraction attraction) async {
    return await attractions.document().setData({
      'atName': attraction.atName,
      'atDiscreption': attraction.atDiscreption,
      'atImageUrl': attraction.atImageUrl,
      'location': attraction.geoPoint,
    });
  }

并且我想将时间轴列表作为子集合写入Firebase？ 我尝试了这种方法，但是没有用：

Future updateTimelinesData(Attraction attraction) async {
    return attraction.timlines.map((e) =>
        attractions.document().collection('timelines').document().setData({
          'date': e.date,
          'discreption': e.descreption,
        }));
  }

PS：我可以将数据作为地图字段直接传递给文档，如以下代码所示：

final CollectionReference attractions =
      Firestore.instance.collection('attractions');

  Future updateAttractionData(Attraction attraction) async {
    List<Map> convertTimlinesToMap({List<Timeline> timlines}) {
      List<Map> timelines = [];
      timlines.forEach((Timeline timeline) {
        Map time = timeline.toMap();
        timelines.add(time);
      });
      return timelines;
    }

    return await attractions.document().setData({
      'atName': attraction.atName,
      'atDiscreption': attraction.atDiscreption,
      'atImageUrl': attraction.atImageUrl,
      'location': attraction.geoPoint,
      //we used a method here because Firebase does not writes list of objects , but it can do map attributes 
      //so we're converting the list of timeline objects to list of maps
      'timeline': convertTimlinesToMap(timlines: attraction.timlines),
    });
  }

但是我正在寻找的是将其作为子集合而不是作为字段传递。