Querying By Multiple Keys in Firebase

Question

I have a list of known keys in my Firebase database

-Ke1uhoT3gpHR_VsehIv
-Ke8qAECkZC9ygGW3dEJ
-Ke8qMU7OEfUnuXSlhhl

Rather than looping through each of these keys to fetch a snapshot of their respective object, how can I query for each of these keys in one single, unified request? Does Firebase provide this?

I've discovered the Promise.all() function which looks promising (no pun intended I swear) but I'm not sure how to implement it using the standard way of fetching firebase data like so

var userId = firebase.auth().currentUser.uid;
return firebase.database().ref('/users/' + userId).once('value').then(function(snapshot) {
  var username = snapshot.val().username;
});

Thanks for any help!

Answer 1

As David's comment suggested: if the items are in some way related, you may be able to built a query to get them all.

Otherwise this would do the trick:

var keys = [ 
  "-Ke1uhoT3gpHR_VsehIv",
  "-Ke8qAECkZC9ygGW3dEJ",
  "-Ke8qMU7OEfUnuXSlhhl"
];
var promises = keys.map(function(key) {
  return firebase.database().ref("/items/").child(key).once("value");
});
Promise.all(promises).then(function(snapshots) {
  snapshots.forEach(function(snapshot) {
    console.log(snapshot.key+": "+snapshot.val());
  });
});

Note that retrieving each item with a separate request is not as slow as you may think, since the requests are all sent over a single connection. For a longer explanation of that, see Speed up fetching posts for my social network app by using query instead of observing a single event repeatedly.