Get specific .childrenCount from Firebase - swift

Question

In my new app (Project Control, iOS App Store ;)) I want users to take part of development decisions. For this I have added a path in my Firebase database called "claps". I would like to enter the number of the following in my TableView for the different concepts. I have tried the following
self.posts.append(Post(title: post_title, des: post_description, info: "\(post_date) - \(post_user) - \(post_claps) 👏", claps: Int(post_claps)))
for var item in self.posts {
g.ref.child("concepts").child(item.title).queryOrdered(byChild: "claps").observe(.childAdded) { (snapshotClaps: DataSnapshot!) in
item.claps = Int(snapshotClaps.childrenCount)
}
}
DispatchQueue.main.async() {
self.tableView.reloadData()
}
However, it does not yet represent the right one, but is one before it. I don't know how to make the reference more specific to really get only what's under claps.
This ist my Database:
Currently my output is 5 but it should be 4. You see its observing one "layer" to early. Help will be appreciated. Improvements too :)
UPDATE:
Through testing I could reveal that the problem is in the reference. The Int five is coming from the 5 Childs of "top-layer" "Journal". My problem is that I cant get any deeper in the structure because I don't have a specific String for .child()

Answer 1

Since you're observing the .childAdded event, your closure gets called for each matching child node. If you want to count the number of matching child nodes, you'll want to observe the .value event, which ensures your closure gets called for all matching nodes at once.
Something like:
g.ref.child("concepts").child(item.title).observe(.value) { (snapshotClaps: DataSnapshot!) in
item.claps = Int(snapshotClaps.childrenCount)
}
Note that I also removed the orderBy clause, since that has no useful meaning if all you use is the count.

Answer 2

create an Array and allow the firebase to populate it. or do something like
g.ref.child("concepts").child(item.title).observe(.value) { (snapshotClaps: DataSnapshot!) in
item.claps = Int(snapshotClaps.childrenCount)
}
observing value makes sure your closure gets its matching nodes.

Answer 3

There's a couple of great solutions but the issue in reading a node by .value is it reads in everything in that node.
While that would be fine for nodes that have a limited amount of data, it would overwhelm the device when the node contains a lot of data.
So another option is to leverage that Firebase executes all .childAdded events before .value events. That way, we can use a .value as a trigger that all nodes have been read.
Here's a function that uses .childAdded to iterate and count all of the users in the users node. Also, there's a .value observer that reads in just the last node, removes the .childAdded observer and passes the count back to the calling function via a completion handler. Remember that even though we are attaching both observers, the .childAdded events will all fire before the .value event.
func countUsers( completion: #escaping(Int) -> Void) {
var count = 0
let usersRef = self.ref.child("users")
usersRef.observe(.childAdded, with: { snapshot in
count+=1
})
let query = usersRef.queryOrderedByKey().queryLimited(toLast: 1)
query.observeSingleEvent(of: .value, with: { snapshot in
usersRef.removeAllObservers()
completion(count)
})
}
to call the function, here's the code
func getUserCount() {
self.countUsers(completion: { userCount in
print("number of users: \(userCount)")
})
}