Javascript 如何从 Firebase 数据快照中获取密钥？

How to get the key from a Firebase data snapshot?

提问by Thomas David Kehoe

I'm able to query my usersarray with an e-mail address and return the user's account info:

我可以users使用电子邮件地址查询我的数组并返回用户的帐户信息：

users.orderByChild('email').equalTo(authData.user.email).once('value').then(function(snapshot) {
        console.log(snapshot.val());
        console.log(snapshot.key); // 'users'
        console.log(snapshot.child('email').key); 'email'
        ...

How do I get the key (-KiBBDaj4fBDRmSS3j0r). snapshot.keyreturns users. snapshot.child('email').keyreturns email. The key doesn't appear to be a child, i.e., it appears to be in between usersand email.

我如何获得密钥 ( -KiBBDaj4fBDRmSS3j0r)。snapshot.key返回users。snapshot.child('email').key返回email。键似乎不是一个孩子，即它似乎在users和之间email。

回答by camden_kid

You could do something like this:

你可以这样做：

var key = Object.keys(snapshot.val())[0];

Ref: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

参考：https: //developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

The Object.keys() method returns an array of a given object's own enumerable properties, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).

Object.keys() 方法返回给定对象自己的可枚举属性的数组，其顺序与 for...in 循环提供的顺序相同（区别在于 for-in 循环将原型链中的属性枚举为好）。

回答by Ernestyno

Realtime database:

实时数据库：

For this you can simple use: snapshot.key

为此，您可以简单地使用：snapshot.key

snapshot = firebase.database.DataSnapshot

快照 = firebase.database.DataSnapshot

this.app.database()
        .ref('/data/')
        .on('value', function(snapshot) {
            const id = snapshot.key;

            //----------OR----------//
            const data = snapshot.val() || null;
            if (data) {
              const id = Object.keys(data)[0];
            }
        });

Firestore:

消防店：

snapshot.id

快照.id

snapshot = firebase.firestore.DocumentSnapshot

快照 = firebase.firestore.DocumentSnapshot

this.app.firestore()
        .collection('collection')
        .doc('document')
        .onSnapshot(function(snapshot) {
            const id = snapshot.id;

            //----------OR----------//
            const data = snapshot.data() || null;
            if (data) {
              const id = Object.keys(data)[0];
            }
        });

回答by Thomas David Kehoe

Similar to camden_kid, I used Object.keys(arr), but in three lines:

与 camden_kid 类似，我使用了Object.keys(arr), 但在三行中：

var arr = snapshot.val();
var arr2 = Object.keys(arr);
var key = arr2[0];
console.log(key) // -KiBBDaj4fBDRmSS3j0r

回答by Renaud Tarnec

users.orderByChild('email').equalTo(authData.user.email)is a Query (doc) that you have built by "chaining together one or more of the filter methods". What is a bit specific with your query is that it returns a dataSnapshot with only one child, since you query with equalTo(authData.user.email).

users.orderByChild('email').equalTo(authData.user.email)是您通过“将一个或多个过滤器方法链接在一起”构建的查询 ( doc)。您的查询有一点特别之处在于它返回一个只有一个孩子的 dataSnapshot，因为您使用equalTo(authData.user.email).

As explained here, in this exact case, you should loop over the returned dataSnapshot with forEach():

正如这里所解释的，在这种确切的情况下，您应该使用以下命令遍历返回的 dataSnapshot forEach()：

Attaching a value observer to a list of data will return the entire list of data as a single snapshot which you can then loop over to access individual children.

Even when there is only a single match for the query, the snapshot is still a list; it just contains a single item. To access the item, you need to loop over the result, as follows:

ref.once('value', function(snapshot) {
  snapshot.forEach(function(childSnapshot) {
    var childKey = childSnapshot.key;
    var childData = childSnapshot.val();
    // ...
  });
});

将值观察者附加到数据列表将返回整个数据列表作为单个快照，然后您可以循环访问单个子项。

即使查询只有一个匹配项，快照仍然是一个列表；它只包含一个项目。要访问该项目， 您需要遍历 result，如下所示：

ref.once('value', function(snapshot) {
  snapshot.forEach(function(childSnapshot) {
    var childKey = childSnapshot.key;
    var childData = childSnapshot.val();
    // ...
  });
});

回答by Karan Prajapati

I found new way to get the data based on snapshot key -

我找到了基于快照键获取数据的新方法 -

 firebase.database().ref('events').once('value',(data)=>{
      //console.log(data.toJSON());
      data.forEach(function(snapshot){
        var newPost = snapshot.val();
        console.log("description: " + newPost.description);
        console.log("interest: " + newPost.interest);
        console.log("players: " + newPost.players);
        console.log("uid: " + newPost.uid);
        console.log("when: " + newPost.when);
        console.log("where: " + newPost.where);
      })
      })