新的云功能和承诺。我尝试在不同的位置添加承诺，但仍然在日志中得到消息。第一，我不确定我应该在哪里添加承诺，第二，我是否应该什么也不回。在调用match（如果条件满足，则创建channel）之后，我不需要执行另一个函数。虽然触发onCreate会有多个用户，所以我想确保每次执行一个用户。

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

//every time user added to liveLooking node
exports.command = functions.database
        .ref('liveLooking/{uid}')
        .onCreate((snap, context) => {
    const uid = context.params.uid
    match(uid)
})
function match(uid) {
    let m1uid, m2uid
    admin.database().ref('liveChannels').transaction((data) => {
        //if no existing channels then add user to liveChannels
        if (data === null) {
            console.log(`${uid} waiting for match`)
            return { uid: uid }
        }
        else {
            m1uid = data.uid
            m2uid = uid
            if (m1uid === m2uid) {
                console.log(`$m1uid} tried to match with self!`)
                //match user with liveChannel user
            } else {
                console.log(`matched ${m1uid} with ${m2uid}`)
                createChannel(m1uid, m2uid) 
                return null
            }
        }
    },
    (error, committed, snapshot) => {
        if (error) {
            throw error
        }
        else {
             return {
                committed: committed,
                snapshot: snapshot
            }
        }
    },
    false)
 }

function createChannel(uid1, uid2) {
    // Add channels for each user matched
    const channel_id = uid1+uid2
    console.log(`starting channel ${channel_id} with uid1: ${uid1}, uid2: ${uid2}`)
    const m_state1 = admin.database().ref(`liveUsers/${uid1}`).set({
        channel: channel_id
    })
    const m_state2 = admin.database().ref(`liveUsers/${uid2}`).set({
        channel: channel_id
    })
}

编辑1-我尝试将事务更改为使用await，这样它将只在事务之后更改UserLife节点。得到这两个警告。1）应在异步函数“match”的末尾返回一个值。2）在***return Arrow函数应返回一个值。如果use与self匹配，我不会尝试在LiveChannels下更改任何内容。不确定如何修复该警告。3）仍然在日志中获得函数返回未定义的、预期的承诺或值--我认为是命令函数。

async function match(uid) {
  let m1uid, m2uid;
  let createChannel = false
  try {
    const transactionResult = await admin
      .database()
      .ref("liveChannels")
      .transaction(
        (data) => {
             if (data === null) {
                 console.log(`${uid} waiting for match`)
                 return { uid: uid }
             }
             else {
                 m1uid = data.uid
                 m2uid = uid
                 if (m1uid === m2uid) {
                     console.log(`$m1uid} tried to match with self!`)
                     ***return***
                 } else {
                     console.log(`matched ${m1uid} with ${m2uid}`)
                     createChannel = true
                     return {}
                 }
             }
        },
        (error, committed, snapshot) => {
             if (error) {
                 throw error
             }
             else {
                  return {
                     committed: committed,
                     snapshot: snapshot
                 }
             }
        },
        false
      );

    if (transactionResult) {
        if (createChannel) {
            const channel_id = m1uid + m2uid
            console.log(`starting channel ${channel_id} with uid1:    ${m1uid}, uid2: ${m2uid}`)
            const m_state1 = admin.database().ref(`liveUsers/${m1uid}`).set({
                channel: channel_id
            })
            const m_state2 = admin.database().ref(`liveUsers/${m2uid}`).set({
                channel: channel_id
            })
            return Promise.all([m_state1, m_state2])
        }
    }
  } catch (err) {
    throw new Error(err);
  }
}