ios - 在Swift中使用Firebase计数看不见的邮件

Question

我正在尝试编写聊天应用程序。

我想计算未查看(看不见)的邮件数量。

我的数据库如下所示:

user-messages
 |
 |_messages
    |
    |_UserID1
    |   |
    |   |_UserID2
    |     |
    |     |_ MessageID1
    |     |_ MessageID2
    |     |_ MessageID3
    |     |_ etc...
    |     
    |_UserID2
    |   |
    |   |_UserID1
    |     |
    |     |_ MessageID1
    |     |_ MessageID2
    |     |_ MessageID3
    |     |_ etc...

对于Messages对象:

messages
 |
 |_messageID1
 |  |
 |  |_ notViewed: false / true
 |  |_ text: "Message text"
 |  |_ timestamp: 1522230692
 |  |_ etc...
 |  
 |_messageID2
 |  |
 |  |_ notViewed: false / true
 |  |_ text: "Message text"
 |  |_ timestamp: 1522230692
 |  |_ etc...

我到达以获得链接到特定用户的所有消息ID:

var REF_MESSAGE = Database.database().reference().child("messages")
var REF_USER_MESSAGE = Database.database().reference().child("user-messages").child("messages")


func fetchUnviewedMessages(withId id: String, completion: @escaping (Int) -> Void ) {

      REF_USER_MESSAGE.child(id).observe(.childAdded) { (snapshot) in

         let userId = snapshot.key as String

         self.REF_USER_MESSAGE.child(id).child(userId).observe(.childAdded, with: { (snapshot) in
            let messageId = snapshot.key

                // This part is where I have a problem
                self.fetchMessageNotViewed(messageId, completion: { (nbMessageNotRead)  in
                   completion(nbMessageNotRead)
                })
             })
          }
    }

但我不知道该如何处理该列表，以观察未见消息的数量...

我尝试过，但是没有成功:

func fetchMessageNotViewed(_ messageId: String, completion: @escaping (Int) -> Void) {
      guard let currentUid = Api.User.CURRENT_USER?.uid else {
         return
      }

      REF_MESSAGE.child(messageId).queryOrdered(byChild: "notViewed").queryEqual(toValue: true).observe(.value, with: { (snapshot) in

         let count = Int(snapshot.childrenCount)
         print(count)
      }, withCancel: nil)
}

Answer 1

我们可以利用复合值来相当轻松地处理此问题。

对Firebase结构消息节点进行简单的更改:

messages
 |
 |_messageID1
 |  |
 |  |_ notViewed: false / true
 |  |_ text: "Message text"
 |  |_ timestamp: 1522230692
 |  |_ forUid_status: "UserId1_unread"   //<- Compound value
 |  |_ etc...
 |  
 |_messageID2
 |  |
 |  |_ notViewed: false / true
 |  |_ text: "Message text"
 |  |_ timestamp: 1522230692
 |  |_ forUid_status: "UserId1_read"   //<- Compound value
 |  |_ etc...

那么一个简单的查询就会显示出UserId1未读消息的数量

let messagesRef = self.ref.child("messages")
let uid = "UserId1"
let status = "unread"
let queryString = uid + "_" + status //results in a string UserId1_unread

let ref = messagesRef.queryOrdered(byChild: "forUid_status").queryEqual(toValue: queryString)
ref.observe(.value, with: { snapshot in
    if snapshot.exists() {
        let count = snapshot.childrenCount
        print("unread messages: \(count)")
    } else {
        print("no unread messages")
    }
})

针对上述Firebase运行此代码会导致

unread messages: 1

这也可能有助于加载未读消息，因为不仅可以获取未读消息的计数，而且将观察者添加到该节点还可以在为UserId1添加新的未读消息时通知应用程序