如何从firebase中的值中获取密钥 [英] How to get the key from the value in firebase

问题描述

当我知道 Firebase 的以下结构中的字段name"包含efg"时，如何获取密钥-KLpcURDV68BcbAvlPFy".

How do I get the key "-KLpcURDV68BcbAvlPFy" when I know the field "name" contains "efg" in the following structure in Firebase.

clubs
    -KLpcURDV68BcbAvlPFy
        dept: "abc"
        desc: "xyz"
        name: "efg"
    -asdasdasddsad
        dept: "asda"
        desc: "asd"
        name: "adddd"

我试过了，但它返回了俱乐部"

I tried this but it returned "clubs"

mDatabase.child("clubs").orderByChild("name").equalTo("efg").addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            String clubkey =dataSnapshot.getKey();

推荐答案

那是因为您正在使用 ValueEventListener.如果查询匹配多个子项，则返回所有这些子项的列表.即使只有一个匹配子项，它仍然是一个列表.由于您在该列表上调用 getKey()，您将获得运行查询的位置的键.

That's because you're using a ValueEventListener. If the query matches multiple children, it returns a list of all those children. Even if there's only a single matches child, it's still a list of one. And since you're calling getKey() on that list, you get the key of the location where you ran the query.

要获取匹配子项的键，请遍历快照的子项:

To get the key of the matches children, loop over the children of the snapshot:

mDatabase.child("clubs")
         .orderByChild("name")
         .equalTo("efg")
         .addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        for (DataSnapshot childSnapshot: dataSnapshot.getChildren()) {
            String clubkey = childSnapshot.getKey();

但请注意，如果您假设俱乐部名称是唯一的，您不妨将俱乐部存储在他们的名称下，然后无需查询即可访问正确的俱乐部:

But note that if you assume that the club name is unique, you might as well store the clubs under their name and access the correct one without a query:

mDatabase.child("clubs")
         .child("efg")
         .addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        String clubkey = dataSnapshot.getKey(); // will be efg

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