ForEach 仅循环遍历 DataSnapshot 上的第一项

Question

我正在尝试遍历 DataSnapshot 的内容，然后根据条件为每个元素做一些工作，但目前，ForEach 只在第一项中工作。 “serverStatus”有时正在等待，有时在“onCall”中。当第一个项目是“onCall”时，不会像我认为应该做的那样遍历其余项目。下面是我从哪里获取信息的快照：

这是我的功能：

exports.manageCallRequests = functions.database.ref('/resquests/{userId}').onCreate((snap, context) => {
    const event = snap.val();

    console.log("function manageCallRequests is being called")
    var rootPath = admin.database().ref();
    var userOnCall = context.params.userId;

    var serversRef = rootPath.child('servers');
     var callRequest = event;
     var userTime = callRequest["time"];
     var waiting= "waiting";

  //We first get all the servers in ascending order depending on the last time they were used
  var serversSorted = serversRef.orderByChild('lastTimeUsed')


       //Gets the children on the "serversSorted" Query
       return serversSorted.once("value").then(allServers =>{
        //Checks if there is any child
            if(allServers.hasChildren()){



                    allServers.forEach(async function(server) {


                        //we extract the value from the server variable, this contains all the information 
                        //about each one of the servers we have
                        var serverInfo = server.val();
                        var serverKey = server.key;
                        var serverNumber = serverInfo["serverNumber"];
                        var serverStatus = serverInfo["serverStatus"];

console.log("server status "+serverStatus)
                        if(serverStatus === waiting){

                            const setCallRequest = await serversRef.child(serverKey).child("current").child("callRequest").set(callRequest);
                            const removeUserOnCall = await rootPath.child("resquests").child(userOnCall).remove();
                            const setServerStatus = await serversRef.child(serverKey).child("serverStatus").set("onCall");

                        }

                    });
                }else{
                    console.log("No servers available")


                }
            });

});

Answer 1

我有相同的行为，因为我的云函数在所有迭代都在 forEach 循环中执行之前退出。我使用这个 sn-p 代码摆脱它：

for (const doc of querySnapshot.docs) {
    // Do wathever you want    
    // for instance:
    await doc.ref.update(newData);
}

Answer 2

我找到了两种方法来完成这项工作。如果我们有一个没有任何 OrderBy* 调用的 DataSnapshot，第一个很有用，在这种情况下，将是：

var allServers = await serversRef.once("value");

for (let serverKey of Object.keys(allServers.val())){
   var server = allServers[serverKey];
    //Do some work
}

我们需要首先获取对象的键，然后才能从 for 循环中提取它，正如 here 所解释的那样，否则我们将得到“TypeError: 'x' is not iterable”

现在这个特殊情况的问题是，a 有一个 DataSnapshot，它之前在 var serversSorted = serversRef.orderByChild('lastTimeUsed') 排序，所以当我们调用 Object.keys(allServers.val()) 时，返回的值不再排序，这就是 forEach() 派上用场的地方。它保证 DataSnapshot 的子项将按照 here 解释的查询顺序进行迭代，但是由于某些原因，在 forEach 循环中执行一些异步工作时，这似乎不起作用，这就是我必须这样做的原因：

var serversSorted = serversRef.orderByChild('lastTimeUsed')
    var allServers = await serversSorted.once("value");

    //Checks if there is any children
    if (allServers.hasChildren()) {
        //if there is iterate through the event that was passed in containing all
        // the servers
        var alreadyOnCall = false;
        var arrayOfServers = []
        var arrayOfKeys = []

        allServers.forEach(function(individualServer){
                arrayOfKeys.push(individualServer.key)
                arrayOfServers.push(individualServer)
        })

        for (var serveIndex = 0; serveIndex < arrayOfServers.length;serveIndex++){

            var serverObj = arrayOfServers[serveIndex]
            var serverObject = serverObj.val()
            var serverKey = arrayOfKeys[serveIndex]

            var serverStatus = serverObject["serverStatus"]; 
            var serverNumber = serverObject["serverNumber"]; 

            console.log("server info "+serverStatus+" "+serverKey);

            if (serverStatus === waiting && alreadyOnCall === false) {
                const setCallRequest = await serversRef.child(serverKey).child("current").child("callRequest").set(callRequest);
                const removeUserOnCall = await rootPath.child("resquests").child(userOnCall).remove();
                const setServerStatus = await serversRef.child(serverKey).child("serverStatus").set("onCall");
                alreadyOnCall= true
                console.log("Call properly set");
            } 
        }


    }