Question

我尝试将聊天功能添加到以Firebase Realtime DB作为存储空间的Android应用中。

我的架构是这样的，

conversation: {
  conversation_id_generated_by_firebase: {
    last_message: {
      message: "hehe"
      type: "text"
      attachments: {0: "url", 1: "url"}
      likes: {0: "uid1", 1: "uid2"}
      created_at: 1245789898
    },
    messages: {
      m1: {
        message: "hehe"
        type: "text"
        attachments: {0: "url", 1: "url"}
        likes: {0: "uid1", 1: "uid2"}
        created_at: 1245789898
      }, m2: {}, m3: {}, m4: {}
    },
    read_till: {
      uid1: 14567894229
      uid2: 14567894228
    },
    created_at: 1456789329
    updated_at: 1456789429
  },
}

现在，如何在一个查询/调用中使用ID获取多个会话？

Answer 1

没有Firebase等同于SQL的SELECT * WHERE id IN (1,2,3)。在Firebase中，您将分别检索每个项目。

这并不像大多数开发人员想象的那么慢，因为Firebase可以通过单个连接有效地管理此类请求。请参阅我的答案，以获得更长的解释（以及一些ASCII艺术）：Speed up fetching posts for my social network app by using query instead of observing a single event repeatedly

Answer 2

通过检索ID，您是否想要检索＆＃34; conversation_id_generated_by_firebase＆＃34;，如果是，我已经实现了一些类似的事情，根据您的数据库详细信息修改了代码。如果您可以提供一些您尝试过的代码，我可以帮助您。

    ArrayList<String> keyList = new ArrayList<>();

    // i am assuming you have Chat Object for each conversation
    ArrayList<Chat> chatList = new ArrayList<>();

    myRef = database.getReference().child("conversation");
    ValueEventListener chatListener = new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
        //will be called every time a new conversation is added

          if(dataSnapshot != null){
              for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {  
                String key = postSnapshot.getKey();

                //store key(your id) in array list
                keyList.add(key);


                //now i am assuming you have an object of chat message
                Chat chat = postSnapshot.getValue(Chat.class);

                //add all conversation to chatList ArrayList
                chatList.add(chat);
               }
           }
        }



        @Override
        public void onCancelled(DatabaseError databaseError) {
         //handle error incase something fails
        }
    };
    myRef.addValueEventListener(chatListener);

如何在一个查询中使用其ID获取多个子项

2 个答案: