How to tell which descendants are changed with on(“child_changed”)

Question

For example, I have following database structure:

/ 
+ users
  + 1
    + items
      + -xxx: \"hello\"
  + 2
    + items

Then;

Answer 1

Andrew Lee gave a nice answer, but I think you should try to use cloud functions. something like this should work:

exports.getPath = functions.database.ref('/users/{id}/items/{itemId}')
.onWrite(event => {
  // Grab the current value of what was written to the Realtime Database.
  const original = event.data.val();
  console.log('user id', event.params.id);
  console.log('item id', event.params.itemId);
});