如何在flutter中使用Firebase检索数据引用？

Question

我正在使用Firebase用flutter（dart）建立带有文章和食谱的应用程序。显然，文章有多个食谱，而一个食谱可以有多个文章（很多到很多）。

我已使用google提供的列在数据库中设置了引用。但是如果我不应该在模型类中使用Firebase.instance，我什至没有考虑如何使用它来填充它。

import 'package:prepmilecookingfeed/model/activity_feed.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

class Activity_Home_Mobile {
  final DocumentReference reference;
  final List<String> activity_feed;
  final String title;


  Activity_Home_Mobile.fromMap(Map<String, dynamic> map, {this.reference})
      : assert(map['title'] != null),
        assert(map['activity_feed'] != null),
        title = map['title'],
        activity_feed = map['activity_feed'];


  Activity_Home_Mobile.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);

//  @override
//  String toString() => "Record<$name:$votes>";

}

final List<String> activity_feed;  
expected => final List<Article> activity_feed; 

class Article {
  final String name;
  final String desc;
  final String likes;
  final String picture_id;
  final String quick_desc;
  final String steps; 
  final DocumentReference reference;

  Article.fromMap(Map<String, dynamic> map, {this.reference})
      : assert(map['name'] != null),
        assert(map['votes'] != null),
        name = map['name'],
        likes = map['name'],
        desc = map['name'],
        picture_id = map['name'],
        quick_desc = map['name'],
        steps = map['votes'];

  Article.fromSnapshot(DocumentSnapshot snapshot)
      : this.fromMap(snapshot.data, reference: snapshot.reference);

//  @override
//  String toString() => "Record<$name:$votes>";

}