Firestore 抛出“onSnapshot() 需要 1 到 4 个参数”

Question

我正在尝试从 firebase 获取所有当前用户未读消息。问题是我onSnapshot()返回以下错误，但它在初始加载时返回我所需的值。如果添加新文档，则onSnapshot(由于该错误， ) 不会再次触发

FirebaseError：函数 Query.onSnapshot() 需要 1 到 4 个参数，但使用 0 个参数调用。

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)
  }

由于我想获取用户参与的所有聊天中的所有未读消息计数，因此我在 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
          })
        }
      })

什么可能导致上述错误？有更好的方法吗？让我知道数据库结构是否必要。任何帮助深表感谢！

Answer 1

根据firebase 的文档，你必须使用onSnapshot()这样的函数：

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().