Firebase Queries and Completion - ios

Question

I'm having some trouble writing a process to allow a user to delete their Firebase account which deletes their account and all the posts that they had in their account including images. I am querying the Users posts in Firebase Database, looping through and deleting them as they come out. In the middle of this loop, I call a function passing in the image URL to delete the image from Firebase storage. The problem I am having is that I can't get an ordered result because of asynchronous stuff. I thought having completion handlers would give it some order. Should I be looking into dispatch groups? Any help is greatly appreciated.
The start of my process with function call:
ref.deleteFirebaseDBUsersPosts(deleter) { (success) -> Void in
if success {
print("The user and their info is completely gone!")
}
}
Function that queries Firebase and loops through users posts and deletes:
func deleteFirebaseDBUsersPosts(uid: String, completion:(success: Bool) -> Void) {
let usersCurrentId = uid
ref.child(“posts”).queryOrderedByChild("uid").queryEqualToValue("\(uid)").observeEventType(.Value, withBlock: {snapshot in
if let snapshot = snapshot.children.allObjects as? [FIRDataSnapshot] {
for snap in snapshot{
print("SNAP: \(snap)")
if let postedImg = snap.childSnapshotForPath("imageUrl").value {
let postImgUrl = postedImg as! String
self.deletingOldUsersImgsFromStorage(postImgUrl) { (success) -> Void in
}
}
let key = snap.key
ref.child(“posts”).child(key).removeValue()
ref.child(“users”).child(usersCurrentId).removeValue()
}
print("COMPLETING")
completion(success: true)
}
})
}
Deleting the image from Firebase Storage:
func deletingOldUsersImgsFromStorage(postImgUrl: String!, completion:(success: Bool) -> Void) {
let deleteImgRef = ref.child(“images”).child("[imageNAME]")
deleteImgRef.deleteWithCompletion({ (error) in
if (error != nil) {
print("DEVELOPER: There was an error when trying to delete the image from Firebase Storage")
} else {
print("IMAGE SUCCESSFULLY DELETED FROM FIREBASE STORAGE")
}
completion(success: true)
})
}

Answer 1

I dealt with a similar challenge when deleting a user and their data from Firebase. I handled it using dispatch groups to delete the user after my methods that deleted their data had completed.
func deleteUsersData(completion: (success: Bool) -> Void) {}
func deleteUsersPhotoUrl(completion: (success: Bool) -> Void) {}
func deleteUserFromFirebase(completion: (success: Bool) -> Void) {}
let group = dispatch_group_create()
dispatch_group_enter(group)
deleteUsersData { (success) in
if success {
dispatch_group_leave(group)
}
}
dispatch_group_enter(group)
deleteUsersPhotoUrl { (success) in
if success {
dispatch_group_leave(group)
}
}
dispatch_group_notify(group, dispatch_get_main_queue()) {
deleteUserFromFirebase({ (success) in
print("Completely deleted user from Firebase")
})
}
Dispatch groups are great for handling situations like this where you only want to perform a task after the other tasks you specified have completed. Here is more info on how to use dispatch groups.