How to get docs for non-currentUsers in Firebase and Vue-CodePudding

I am attempting to built a chat app with Vue, Firebase Firestore and Firebase authentication. After registering a user, logging in, and submitting a message, I am using the getMessage function below to retrieve the messages from a collection assigned to a doc for the currently logged-in user.

const messages = ref([])

const getMessages = () => {
firebase.firestore().collection("users").doc(firebase.auth().currentUser.uid).collection('messages').orderBy('timestamp')
      .onSnapshot(snap => {
        messages.value = []
        snap.forEach(doc => {
          var msg = doc.data();
          msg.id = doc.id;
          messages.value.push(msg)
        })
      }) 
    },

However, I have multiple registered users and am wanting to retrieve messages for all the users, not just the currentUser. How can I set up the above firestore collection method chain to retrieve messages for all of the registered users, not just currentUser?

CodePudding user response：

You can use Collection Group query here that'll fetch messages from all users as per your use case.

const messages = ref([])

const getMessages = () => {
  firebase.firestore().collectionGroup("messages").orderBy('timestamp')
    .onSnapshot(snap => {
      const messages = snap.docs.map((doc) => ({
        messageId: doc.id,
        userId: doc.parent.parent.id,
        ...doc.data()
      }))

      messages.value = messages
    })
}

Do make sure your security allow users to add message to their sub-collection only but let everyone read them. For example,

rules_version = '2';
service cloud.firestore {
  match /databases/{database}/documents {
    match /{userId=**}/messages/{messageId} {
      allow read: if request.auth == userId; 
    }
 
    match /users/{userId}/messages/{messageId} { 
      allow write: if request.auth.uid == userId;
    }
  }
}

Checkout the documentation for more information about security rules.