Fetch Firebase inside another fetch - ios

Question

So I am creating a forum inside my app and when fetching the topics on the database I also need to fetch some user info like picture and username of the original poster to put it on the table view cells.
To keep the recommendation of keeping the Firebase database flat I have the messages on a separate ref searchable by key and NOT as a child of topics.
I can't keep something like opImage and opUsername as childs of topics because if a user changes its username or profile image I would need to change it on every topic he ever participated as well.
What is the best way to handle this?
The method to fetch from Firebase would look something like this. The problem with that implementation is that the Firebase calls are asynchronous and there would be no guarantee that the image would be attached to the correct topic.
DataService.ds.Topics_Base.child(cat.key!).observeSingleEvent(of:.value, with: { (snapshot) in
if let snapshots = snapshot.children.allObjects as? [FIRDataSnapshot] {//snapshots = all topics
for top in snapshots{
if let dict = top.value as? Dictionary<String,AnyObject>{
guard let title = dict["title"] as? String,let text = dict["text"] as? String,let time = dict["time"] as? String,let username = dict["username"] as? String,let timeSimple = dict["time-simple"] as? String,let lastPost = dict["last-post"] as? String,let open = dict["open"] as? Bool else{
continue
}
let newTopic = Topic(subject: title, text: text, time: time, topicKey: top.key, username: username)
self.allTopics.append(newTopic)
print(self.allTopics.count)
if let email = dict["email"] as? String{
//FETCH USER INFO FROM EMAIL FETCHED
let validEmail = HelperMethods.removeSpecialCharactersFromEmail(email: email)
DataService.ds.Users_Base.child(validEmail).observeSingleEvent(of: .value, with: {(snapshot) in
if let userDict = snapshot.value as? Dictionary<String,AnyObject>{
if let imgUrl = userDict["profile_image_url"] as? String{
self.allTopics[currentIndex].opImageUrl = imgUrl
}
self.allTopics.append(newTopic)
if (totalTopics == snapshots.count){
DispatchQueue.main.async {
self.allTopics.sort { $0.lastPostTime! > $1.lastPostTime!}
self.tableView.reloadData()
self.refreshControl.endRefreshing()
}
}
}
})
}
} }
}
}
)
}
Thanks in advance.

Answer 1

I ended up deciding to fetch the user info AFTER fetching all topics and then looping through the topics array and attaching user info for each topic.
EXAMPLE:
1 - fetch all topics and create array
2 - for each topic in array{
fetch user on Firebase using a property like topic.email
set something like:
topic.imageUrl = user.imageUrl
topic.username = user.username
}
reload table view