如何访问Firebase Realtime数据库中的子节点的父节点？

Question

My Firebase Database Image 在Firebase的实时数据库中，我试图访问被赋予子节点名称的父节点名称。但是，.parent似乎需要对子节点的引用，没有父节点的名称，我似乎无法获得它。

这是我的数据的代码：

<script src="https://www.gstatic.com/firebasejs/5.7.3/firebase.js"></script>
<script src="https://apis.google.com/js/platform.js" async defer></script>

<style>
    tr:hover {background-color: #f5f5f5;}
    th, td {
        border-bottom: 1px solid #ddd;
    }

</style>
<script>

    // Initialize Firebase

var config = {     apiKey：“ AIzaSyA85okZdA9v_XAa9BgJJ2EOdUEbL09k0uY”，     authDomain：“ fir-test-bcb6d.firebaseapp.com”，     databaseURL：“ https://fir-test-bcb6d.firebaseio.com”，     projectId：“ fir-test-bcb6d”，     storageBucket：“ fir-test-bcb6d.appspot.com”，     messagesSenderId：“ 976121809263”   };   firebase.initializeApp（config）;

    // Check to see if you are logged in
    firebase.auth().onAuthStateChanged(function(user) {
        if (user == null) {
            alert("Not logged in.");
            return;
        } else {
            userId = user.uid;
            name = user.displayName;
            imageUrl = user.photoURL;
            email = user.email;
            var user = firebase.auth().currentUser;
            var newuser = user.getAdditionalUserInfo

            user.sendEmailVerification().then(function() {
            // Email sent.
            }).catch(function(error) {
            // An error happened.
            });
            if (firebase.auth().currentUser.emailVerified) {
                alert('Email Verified');
                console.log('Email Verified');
            }

            // write user data to users
            //writeUserData(userId, name, email, imageUrl);
            // moved to tweet function

            // write data to document
            mydiv = document.getElementById("mydata");
            mydiv.innerHTML = name
            myphotodiv = document.getElementById("myphoto");
            myphotodiv.innerHTML = "<img src='" + imageUrl + "'/>";

            firebase.database().ref('/tweets').once('value').then(function(snapshot) {
                var data = (snapshot.val());
                if (data == null) {
                  console.log("No data found at /tweets/" + userId);  
                } else {

                  firebase.database().ref('/users').once('value').then(function(snapshot) { 
                    var userdata = (snapshot.val());
                    if (userdata != null) {
                       dataarray = [data,userdata]
                       console.log(dataarray)
                       updatetweets(dataarray); 
                    }
                  });
                  //console.log(data)
                  //updatetweets(data);
                }
            });
        } // end user null check
    }); // end check auth state

    function encodeImageFileAsURL() {

        var filesSelected = document.getElementById("inputFileToLoad").files;
        if (filesSelected.length > 0) {
            var fileToLoad = filesSelected[0];
            var fileReader = new FileReader();
            fileReader.onload = function(fileLoadedEvent) {
                var srcData = fileLoadedEvent.target.result; // <--- data: base64
                //var newImage = document.createElement('img');
                //newImage.src = srcData;
                //document.getElementById("imgTest").innerHTML = newImage.outerHTML;
                document.getElementById("imgTest").innerHTML = srcData;
                //console.log("Converted Base64 version is: " + document.getElementById("imgTest").innerHTML);
                //console.log(srcData);
            }
            fileReader.readAsDataURL(fileToLoad);
        }
    } // end function

    // write user data
    function writeUserData(userId, name, email, imageUrl) {
        firebase.database().ref('users/' + userId).once('value',    function(snapshot) {
             if (!snapshot.exists()) {
                firebase.database().ref('users/' + userId).set({
                    username: name,
                    email: email,
                    profile_picture : imageUrl
                }); 
             }                                      
        });
    }


    function updatetweets(data) {
        var tweetnumber = 0;
        //var mylist = "<ul>";
        var mytab = "<table id='tweettable'>";
        users = data[1]; // put on top, because changed data - not good coding change later
        data = data[0];


        for (var u in data) {
            for (var t in data[u]) {
                mytab = mytab + "<tr>";
                var date = new Date(data[u][t].time);
                var time = date.toString();                    
                if (data[u][t].img != "") {
                    mytab = mytab + "<td><img src='" + users[u].profile_picture + "' width='50px'></td>";
                    mytab = mytab + "<td>" + users[u].email + "</td>";
                    mytab = mytab + "<td>" + data[u][t].tweet + "</td>";
                    mytab = mytab + "<td>" + time + "<br><img src='" + data[u][t].img + "' width='300px'></td>";
                    mytab = mytab + "<td><p>Like this tweet</p>" + "<button id=" + t + " onclick=" + "like(this.id)" + ">Like</button>" + "<p>Likes: </p>" + "<p id='" + t + "likes'" + "'>" + data[u][t].likes + "</p>" + "</td>";

                } else {
                    mytab = mytab + "<td><img src='" + users[u].profile_picture + "' width='50px'></td>";
                    mytab = mytab + "<td>" + users[u].email + "</td>";
                    mytab = mytab + "<td>" + data[u][t].tweet + "</td>";
                    mytab = mytab + "<td>" + time + "</td>";
                    mytab = mytab + "<td><p>Like this tweet</p>" + "<button id=" + t + " onclick=" + "like(this.id)" + ">Like</button>" + "<p>Likes: </p>" + "<p id='" + t + "likes'" + "'>" + data[u][t].likes + "</p>" + "</td>";
                } 
                mytab = mytab + "</tr>";
            }   
        }
        //mylist = mylist + "</ul>";
        mytab = mytab + "</table>"
        var mytdiv = document.getElementById("mytweets");
        //mytdiv.innerHTML = mylist;
        mytdiv.innerHTML = mytab;
    }

    // write tweets to firebase
    function tweet() {

        var twitdoc = document.getElementById("twit");
        var twitimg = document.getElementById("imgTest");
        var nameValue = twitdoc.value;
        var imgValue = twitimg.innerHTML;
        var d = new Date();
        var dayofweek = d.getDay();
        console.log(dayofweek);
        var weekdays = ["Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday"];
        var dayofmonth = d.getDate();
        var monthnumber = d.getMonth();
        var monthnames = ["January", "February", "March", "April", "May", "June", "July", "August", "September", "October", "November", "December"];
        var year = d.getFullYear();
        var thedate = weekdays[dayofweek] + ", " + monthnames[monthnumber] + " " + dayofmonth + ", " + year;
        console.log(thedate);
        var hours = d.getHours();
        var minutes = d.getMinutes();
        if (hours < 12) {
            var time = 
        }
        var js_time = Date.now();
        //var numberoffollowers = 2;
        var tweetid = firebase.database().ref('tweets/' + userId + "/").push({tweet: nameValue, time: js_time, date: thedate, img: imgValue, likes: 0});
        //var followers = firebase.database().ref('users/' + userId + "/").push({followers: numberoffollowers});
        twitdoc.value = "";
        writeUserData(userId, name, email, imageUrl);
        console.log("tweet written")

        firebase.database().ref('/tweets').once('value').then(function(snapshot) {
                var data = (snapshot.val());
                if (data == null) {
                  console.log("No data found at /tweets/" + userId);  
                } else { 
                    firebase.database().ref('/users').once('value').then(function(snapshot) { 
                    var userdata = (snapshot.val());
                    if (userdata != null) {
                       dataarray = [data,userdata]
                       console.log(dataarray)
                       updatetweets(dataarray); 
                    }
                  });
                }
            });



        // The unique key stored in tweetid is based on a timestamp, so list items will automatically be ordered chronologically. Because Firebase generates a unique key for each tweet, no write conflicts will occur if multiple users add a post at the same time. https://firebase.google.com/docs/database/admin/save-data

    }

    function like(t) {
        alert(t);
        console.log('tvalue' + t);
        console.log(t.ref());

        var y = firebase.database().ref('/tweets/' + userId + "/" + t);
        var parent = y.parent;
        console.log('Parent: ' + parent);
        var res = String(parent);
        console.log(res);
        var goal = res.substring((res.length - 28), res.length);
        console.log(goal);



        var oldlikes = document.getElementById(t + "likes").innerHTML;
        console.log(oldlikes);
        firebase.database().ref('/tweets/' + goal + "/" + t).once('value', function(snapshot) {
           console.log("/tweets/" + goal + "/" + t);
           console.log(snapshot.val());
           var oldlikenumber = snapshot.val().likes;
           console.log(oldlikenumber);
           var newlikes = oldlikenumber + 1;
                var tweetid = firebase.database().ref('tweets/' + goal + "/" + t).update({likes: newlikes});
                    console.log(newlikes);
            document.getElementById(t + "likes").innerHTML = newlikes;
                });


        /* console.log('liked tweetnumber' + tweetnumber);
        alert('liked tweetnumber' + tweetnumber);
        document.getElementById('tweetnumber' + tweetnumber).innerHTML = "Likes: " + 1;*/
    }

    //function follow {

    //}

    function signin() {
        console.log("Signing in");
        var provider = new firebase.auth.GoogleAuthProvider();
        firebase.auth().signInWithRedirect(provider).then(function(result) { 
            window.location.replace("fbtest.html");
        });
    }

    function signout() {
        console.log("Signing out");
        firebase.auth().signOut().then(function() {
        });
    }



</script>

<body>
    <button onclick="signin()">Sign in</button>
    <button onclick="signout()">Sign out</button>
    <br>
    <p>Step 1: delete your existing Firebase Realtime database</p>
    <a href="fbtest.json" target="_target">Step 2: replace JSON Firebase rules for database</a><br>

    <form>
        Tweet:<br>
        <textarea id="twit" type="text" name="thetweet" cols="100" rows="4"></textarea>
    </form> 
    <button type="button" onclick="tweet()">Submit</button>

    <br><input id="inputFileToLoad" type="file" onchange="encodeImageFileAsURL();" />
    <div id="imgTest" style="display:none;"></div>

<div id="mytweets"></div>
<div id="mydata"></div>
<div id="myphoto"></div>




</body>

问题出在like函数中：第一部分是var y，如果我能找到一种方法来获取推特参数t所表示的推文的人的用户ID，那么所有这些都是不必要的。

如果我可以获取该人的userId（无论我需要什么= userId），那么我可以写：

firebase.database（）。ref（'/ tweets /'+任意+“ /” + t）.once（'value'，function（snapshot）{

//相同的东西

var tweetid = firebase.database（）。ref（'tweets /'+任意+“ /” + t）.update（{likes：newlikes}）;

Answer 1

尽管该问题已经存在一年了，并且可能是一个XY问题，但正如评论所述，我相信这可能会回答您的特定问题。我不知道直接父项时唯一以子项引用结尾的方法是是否通过查询检索了孩子的孩子，在这种情况下，可以使用.ref从documentSnapshot获取父节点。 .key，就像这样：

database().ref("/users/").orderByChild("name").startAt(someText).once('value')
          .then(querySnapshot => {

               querySnapshot.forEach(docSnapshot => {

                   console.log("parent = " + docSnapshot.ref.key);

                   // if this docSnapshot was retrieved because of child "name"'s value
                   // at https://someapp-firebaseio.com/users/uid8234/name
                   // then docSnapshot.ref.key == uid8234

               })
          })

例如，如果将用户数据存储在/ users /中的uid节点下，并且使用“名称”作为每个uid节点的子代之一，则可能会发生这种情况。当然，为避免检索到该错误，您还可以将uid的一个额外副本存储在“名称”旁边的另一个键中，并对其进行引用。