如何有效地管理 Firebase 文档中观察者/听众的数量？

Question

假设我在 Cloud Firestore 中有一组文档。我希望人们观察这些文件，但我不希望超过 100 人在任何时间点观察同一份文件。我如何有效地跟踪这一点？

我最初考虑通过管理每个文档中的一组用户 ID 来跟踪观察者/听众的数量。实际上，用户会在观察/收听之前将他们的 ID 添加到这个数组中（或者如果这个数组太大则被拒绝），并在他们停止时从这个数组中删除他们的 ID。这样做的问题是，如果从数组中删除此 ID 的调用失败，我不能仅仅阻止用户离开。如果他们以某种方式终止了应用程序并且删除他们的 ID 的调用没有通过怎么办？

这个问题有更合理的解决方案吗？这可以通过实时数据库或云函数解决吗？谢谢！

Answer 1

我不确定，但请尝试用 Google 搜索 Firebase 访问规则。我认为您可以管理此范围内的访问。
我讲这个规则。

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{document=**} {
      allow read, write: if true;
    }
  }
}

抱歉以这种方式回答，我没有创建 cmets 所需的声誉

Answer 2

已解决！非常感谢 Renaud Tarnec 的原始评论引用了我尚未看到的文档。我在 Google 搜索中遗漏了关键字“存在”。如果您觉得这个答案有帮助，请点赞他的评论！

解决方案：使用https://firebase.google.com/docs/firestore/solutions/presence

斯威夫特：

var connectionReference: DatabaseReference = Database.database().reference(withPath: ".info/connected")
var personalReference: DatabaseReference?
var connectionIssued: Bool = false

func connect(room: String) {
    // Remove any existing observations to ensure only one exists.
    connectionReference.removeAllObservers()
    // Start observing connection.
    connectionReference.observe(.value) { (isConnected) in
        if isConnected.value as! Bool {
            // Connected!
            // Use Bool connectionIssued to ensure this is run only once.
            if !self.connectionIssued {
                self.connectionIssued = true
                self.personalReference = Database.database().reference(withPath: "OnlineUsers/\(userID)")
                // Set onDisconnect before setting value.
                self.personalReference!.onDisconnectRemoveValue()
                self.personalReference!.setValue(room)
                // Now the user is "online" and can proceed.
                // Allow user to "enter" room.
            } else {
                // Connection already issued.
            }
        } else {
            // The user has either disconnected from an active connection or they were already disconnected before connect() was called.
            // Stop observing connection.
            self.connectionReference.removeAllObservers()
            // If the user disconnects after they have entered a room, kick them out.
            if self.connectionIssued {
                // User lost connection.
                kickUserOutOfRoom()
                self.connectionIssued = false
            } else {
                // User cannot log in.
            }
        }
    }
}

// Call when users leave a room when still connected.
func leaveRoomManually() {
    // Remove connection observation.
    connectionReference.removeAllObservers()
    // Attempt to remove "online" marker in database.
    personalReference?.removeValue(completionBlock: { (error, reference) in
        if error != nil {
            // Removal failed, but that should be okay!
            // onDisconnect will still be called later!
            // This failure might result in ghost users if the user proceeds to join another room before disconnecting.
            // Consider writing an onUpdate() cloud function in conjunction with the following onCreate() and onDelete() cloud functions to take care of that case.
        } else {
            // "Online" marker removed from database!
            // We can now cancel the onDisconnect()
            self.personalReference?.cancelDisconnectOperations()
        }
    })
    leaveRoom()
}

云函数（javascript）：

以下云函数会更新 Cloud Firestore 中各个房间的客人人数。

const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp();

const firestore = admin.firestore();

exports.userCameOnline = functions.database.ref('/OnlineUsers/{userID}').onCreate(
    async (snapshot, context) => {
        const room = snapshot.val();
        const guestCountRef = firestore.doc(`Rooms/${room}`);
        return guestCountRef.update({
            Guests: admin.firestore.FieldValue.increment(1)
        });
    });

exports.userWentOffline = functions.database.ref('/OnlineUsers/{userID}').onDelete(
    async (snapshot, context) => {
        const room = snapshot.val();
        const guestCountRef = firestore.doc(`Rooms/${room}`);
        return guestCountRef.update({
            Guests: admin.firestore.FieldValue.increment(-1)
        });
    });