Firebase query not executing in the correct order? - ios

Question

I fetch data and display in a tableView, the problem is the data is not executing in the correct order.
I have tried:
for case let child as DataSnapshot in data!.children.reversed() {
let newDispatchGroup = DispatchGroup()
let commentID = child.key
let uid = child.childSnapshot(forPath: "UID").value as! String
let commentText = child.childSnapshot(forPath: "Comment").value!
let timeStamp = child.childSnapshot(forPath: "timeStamp").value!
let date = ConvertDate(mediaTimestamp: timeStamp as! Double).getDate!
//print(date, "dsfsdafdasfdsafdsahjkfhfdsafsajkadhffdsfsafsasjkfhsdajkhfdsajkhfjklads")
newDispatchGroup.enter()
ref.child("users2").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
print(snapshot, "dshjkfhjkadhfsjkfhsdajkhfdsajkhfjklads")
print(date, "dsfsdafdasfdsafdsahjkfhfdsafsajkadhffdsfsafsasjkfhsdajkhfdsajkhfjklads")
let username = snapshot.childSnapshot(forPath: "username").value
let profileImage = snapshot.childSnapshot(forPath: "profileImage").value
let newUser = User(theuserID: uid, theUsername: username as! String, theprofImage: profileImage as! String)
let newComment = Comment(newUser: newUser, text: commentText as! String, timeStamp: date, NcommentID: commentID)
self.commentsVC1.arrayOfComments.append(newComment)
newDispatchGroup.leave()
//completion()
})
newDispatchGroup.notify(queue: .main, execute: {
print(self.totalComments, "COgfdsdfgfdsgdsfgdfsgfdsgdfsgdskj", self.commentsVC1.arrayOfComments.count)
if self.totalComments == self.commentsVC1.arrayOfComments.count {
print("COmejkfbdshkafdsagfhksdagfdsakj")
self.commentsVC1.tableView.reloadData()
}
})
}
})
}
But it did not work either, the order in which the second firebase calls execute is incorrect.

Answer 1

You should set up your notify closure when you set up your DispatchGroup. And you would not need to use a completion closure for you loadComments function.
let dispatchGroup = DispatchGroup()
dispatchGroup.notify(queue: .main, execute: {
if self.totalComments == self.commentsVC1.arrayOfComments.count {
print("COmejkfbdshkafdsagfhksdagfdsakj")
self.commentsVC1.tableView.reloadData()
}
})
loadComments()
notify will be called, when leave has been called the same amount of times as enter. In your code the last leave call is happening before you have set the anything to be notified about.

Answer 2

I solved with this:
for case let child as DataSnapshot in snap.children.reversed() {
let commentID = child.key
let uid = child.childSnapshot(forPath: "UID").value as! String
let commentText = child.childSnapshot(forPath: "Comment").value!
let timeStamp = child.childSnapshot(forPath: "timeStamp").value!
let date = ConvertDate(mediaTimestamp: timeStamp as! Double).getDate!
let newUser = User(theuserID: uid)
let newComment = Comment(newUser: newUser, text: commentText as! String, timeStamp: date, NcommentID: commentID)
self.commentsVC1.arrayOfComments.append(newComment)
ref.child("users2").child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
let username = snapshot.childSnapshot(forPath: "username").value
let profileImage = snapshot.childSnapshot(forPath: "profileImage").value
let newUserIner = User(theuserID: uid, theUsername: username as! String, theprofImage: profileImage as! String)
newComment.user = newUserIner
if self.totalComments == self.commentsVC1.arrayOfComments.count {
self.commentsVC1.tableView.reloadData()
}
})
}
I would use dispatch group here though so one does not have have to check if its done unnecessarily.