Firebase how to find child knowing its id but not its parent's id (js)

问题

I have a firebase realtime database (not cloud) structure like:

users
  kasdf872ajsda   //user id
     auiiq6d182g1   //list id
        c: <mycontent>   //list content

i know the list id (in this case auiiq6d182g1) and i want to retrieve <mycontent>, but i don't know the user id kasdf872ajsda , because what i'm going to retrieve is probably not from the user currently using the website (and i'm not setting any database rules for "read" in fact, only for "write" is that correct?).

What i'm doing right now is this (not working):

var ref = firebase.database().ref().child('users');
ref.child(listID).once("value", function(snapshot) {
  var snap = snapshot.val();
  myContent = snap.c;
});

回答1:

You could put your reference to users first: var ref = firebase.database().ref('users');

Then loop through:

ref.once('value').then((snapshot)=>{
   snapshot.forEach(function(data) {
      if (data.key == <YOUR_LIST_ID>) {
         //you can access data.c here...
      }
  });
});  

回答2:

Found the solution, if someone should encounter the same issue:

ref.once("value", function(snapshot) {
      snapshot.forEach(function(data) {
        snap = data.child(<YOUR_LIST_ID>).child('c').val();
        if (snap != null){
          myContent = snap;
        }
      });
});

also ref contrary to what everyone says has to be:

var ref = firebase.database().ref().child('users');

this doesn't work:

var ref = firebase.database().ref('users');

来源：https://stackoverflow.com/questions/52782070/firebase-how-to-find-child-knowing-its-id-but-not-its-parents-id-js