iOS callback if firebase query doesn't run (Swift Firebase) - ios

Question

I have a query running to check .childAdded at a location in my database.
It works well when data is found, however, if there is not data at the location, it can't fire the query and therefore this does not allow me to use snapshot.exists because it doesn't even run the query.
This is my current code
let favouriteRef = self.databaseRef.child("users").child(userID!).child("Favourites")
// Code doesn't run past this line when no data at location
favouriteRef.queryOrderedByKey().observe(.childAdded, with: { (snapshot) in
let favouriteID = "\(snapshot.value!)"
let usersRef = self.databaseRef.child("users")
usersRef.observeSingleEvent(of: .value, with: { (users) in
for user in users.children {
let favCleaner = UserClass(snapshot: user as! DataSnapshot)
if favouriteID == favCleaner.uid {
tempFav.append(favCleaner)
}
}
self.hasFavourites = true
self.tableView.reloadData()
self.usersArray = tempFav
self.collectionView.reloadData()
})
})
I would like to find a way to receive a callback if the query doesn't run (no data at location)
Thanks.

Answer 1

If there is absolutely no data at the location, then obviously this event trigger is not sufficient for you to get the data because this event only gets triggered when something gets added.
So you have two options
Add another trigger of type .observeSingleEvent(of: .value, with: { (snapshot) in
// Get the values and write the relevant actions
}
Or you can update this event to type .observe(.value, with: {snapshot in // write the relevant code
}
Both approaches have their advantage and disadvantage.
First approach will need you to write more code while minimising the number of triggers from your database to your UI. In second approach, there will be more triggers to the UI but it can be fairly easy to code.
From what I can see, you are first trying to establish whether data exists in the favorite node of your database and then comparing it to another snapshot. So if the number of delete or update events are relatively small, my suggestion is to go for approach two.