javascript - Firestore 抛出 'onSnapshot() requires between 1 and 4 arguments'

Question

我正在尝试从 firebase 获取所有当前用户未读的消息。问题是我的 onSnapshot() 返回了以下错误，但它在初始加载时返回了我需要的值。如果添加了新文档，则 onSnapshot() 不会因为该错误而再次触发

FirebaseError: Function Query.onSnapshot() requires between 1 and 4arguments, but was called with 0 arguments.

这是接收所有当前用户未读消息的辅助函数。

async getUnseenMessagesCount() {
    const collectionRef = (await firestore()).collection(this.collectionPath) //chats/${user_id+second_identifier/messages}
    let allMessagesCount = 0
    let currentUserReadMessagesCount = 0
    try {
      collectionRef.onSnapshot().then(snapshot => {
        allMessagesCount = snapshot.docs.length
      })
      collectionRef
        .where('seenBy', '==', '') // compare against empty string because seenBy is userId.
        .onSnapshot()
        .then(snapshot => {
          currentUserReadMessagesCount = snapshot.docs.length
        })
    } catch (error) {
      console.log(error)
    }

    console.log(allMessagesCount)
    console.log(currentUserReadMessagesCount)
    console.log(allMessagesCount - currentUserReadMessagesCount)
  }

因为我想从用户参与的所有聊天中获取所有未读消息计数，所以我在我的 vuex 操作中执行以下操作，该操作在身份验证状态更改时激活:

new UserChatsDB(newUser.id).readAll().then(snapshot => { //users/id/chats/{chat_id: user_id+second_identifier}
        if (snapshot.length > 0) {
          snapshot.forEach(element => {
            console.log(element)
            const count = new MessagesDB(
              element.chat_id
            ).getUnseenMessagesCount()
            console.log(count) //Returns pending Promise
          })
        }
      })

什么会导致上述错误？有更好的方法吗？让我知道是否需要数据库结构。非常感谢任何帮助!

Answer 1

根据docs对于 firebase，您必须像这样使用 onSnapshot() 函数:

async getUnseenMessagesCount() {
    const collectionRef = (await firestore()).collection(this.collectionPath) //chats/${user_id+second_identifier/messages}
    let allMessagesCount = 0
    let currentUserReadMessagesCount = 0
    try {
      collectionRef.onSnapshot(snapshot => {
        allMessagesCount = snapshot.docs.length
      })
      collectionRef
        .where('seenBy', '==', '') // compare against empty string because seenBy is userId.
        .onSnapshot(snapshot => {
          currentUserReadMessagesCount = snapshot.docs.length
        })
    } catch (error) {
      console.log(error)
    }

    console.log(allMessagesCount)
    console.log(currentUserReadMessagesCount)
    console.log(allMessagesCount - currentUserReadMessagesCount)
  }

所以你必须删除你的then()。