Firebase update child values is removing children - ios

Question

I'm trying to handle following and unfollowing in my social media app using Firebase. I have a bar button item entitled "Follow". When tapped, it checks the current follow status(retrieved in viewDidLoad), and calls the follow/unfollow methods accordingly. user represents the owner of the page, and the person the currentUser wants to follow/unfollow.
Unexpected behavior: When following a user a second time, you can watch the proper child nodes in the database appear, then disappear. They should not be disappearing. I have refreshed the page to ensure that the nodes are in fact being deleted somehow. It works properly on the first try after every app launch.
Here is my viewDidLoad(responsible for retrieving currentUserIsFollowing). I suspect the issue lies here:
override func viewDidLoad() {
super.viewDidLoad()
let userDogRef = Database.database().reference().child("users").child(user.uid!).child("dogs")
let followingRef = Database.database().reference().child("users").child((Auth.auth().currentUser?.uid)!).child("following")
followingRef.observeSingleEvent(of: .childAdded) { (snapshot) in
if snapshot.value == nil {
print("no following found")
return
}
let value = snapshot.value as? NSDictionary
let followingUserUID = String(describing: value!["uid"]!)
if self.user.uid == followingUserUID {
self.currentUserIsFollowing = true
DispatchQueue.main.async {
self.followBarButtonItem.title = "Unfollow"
}
}
}
}
Here is the action called when the Follow/Unfollow button is tapped:
#IBAction func followUserButtonPressed(_ sender: Any) {
if !currentUserIsFollowing {
followUser()
return
}
if currentUserIsFollowing {
unfollowUser()
return
}
}
Here is the followUser() method:
fileprivate func followUser() {
let followingRef = Database.database().reference().child("users").child((Auth.auth().currentUser?.uid)!).child("following")
let followersRef = Database.database().reference().child("users").child(user.uid!).child("followers")
followingRef.childByAutoId().updateChildValues(["uid": user.uid as Any]) { (error, ref) in
if error != nil {
print(String(describing: error?.localizedDescription))
}
}
followersRef.childByAutoId().updateChildValues(["uid": Auth.auth().currentUser?.uid as Any]) { (error, ref) in
if error != nil {
print(String(describing: error?.localizedDescription))
}
}
}
Here is the unfollowUser() method:
fileprivate func unfollowUser() {
let followingRef = Database.database().reference().child("users").child((Auth.auth().currentUser?.uid)!).child("following")
let followersRef = Database.database().reference().child("users").child(user.uid!).child("followers")
followingRef.observeSingleEvent(of: .childAdded, with: { (snapshot) in
if snapshot.value == nil {
print("no following found")
}
let value = snapshot.value as? NSDictionary
let followingUserUID = String(describing: value!["uid"]!)
if self.user.uid == followingUserUID {
snapshot.ref.removeValue()
}
})
followersRef.observeSingleEvent(of: .childAdded, with: { (snapshot) in
if snapshot.value == nil {
print("no followers found")
}
let value = snapshot.value as? NSDictionary
let followerUserUID = String(describing: value!["uid"]!)
if Auth.auth().currentUser?.uid == followerUserUID {
snapshot.ref.removeValue()
}
})
}
Here is a photo of my JSON tree:

Answer 1

There's quite a bit going on here to unpack, but I tried my best to follow along and come up with a solution. For one, instead of having two functions, create a single function that handles following and unfollowing:
#IBAction func followUserButtonPressed(_ sender: Any) {
followOrUnfollow()
}
In that function, listen once to the value of the child you need. Instead of using childByAutoId, use the uid as the key and anything as the value. I just used true. This means you can observe the reference directly instead of having to iterate through all the children looking for the one follower. If the child's data is nil, then the user isn't following yet, so the database is updated to follow. If the child's data is not nil, the data is removed.
func followOrUnfollow() {
let followingRef = Database.database().reference().child("users/\(Auth.auth().currentUser?.uid)!/following/\(user.uid!)")
let followersRef = Database.database().reference().child("users/\(user.uid)!/followers/\(Auth.auth().currentUser?.uid)!")
followingRef.observeSingleEvent(of: .value, with: { (snapshot) in
if snapshot.value == nil {
print("no following found")
followingRef.updateChildValues([user.uid: "true"]) { (error, ref) in
if error != nil {
print(String(describing: error?.localizedDescription))
}
}
} else {
print("unfollowing")
snapshot.ref.removeValue()
}
})
followersRef.observeSingleEvent(of: .value, with: { (snapshot) in
if snapshot.value == nil {
print("no followers found")
followersRef.updateChildValues([Auth.auth().currentUser?.uid: "true"]) { (error, ref) in
if error != nil {
print(String(describing: error?.localizedDescription))
}
}
} else {
print("unfollowing")
snapshot.ref.removeValue()
}
})
}
Now there may be some syntactical errors because I'm working on this blindly, but this is the gist of what I would recommend. You will likely have to tweak this to meet your needs.

Answer 2

I'll select Jen's answer as the correct one, but I want to add my working code. I had to make some changes to implement my vision. You can't compare a snapshot.value to nil, so instead you should use if snapshot.exists(). In order to avoid adding a whole new child at the reference point using ref.updateChildValues(), I used .setValue("true"). This just adds a new key-value pair to the "following" and "followers" nodes at the ref.
func followOrUnfollow() {
let followingRef = Database.database().reference().child("users/\(Auth.auth().currentUser!.uid)/following/\(self.user.uid!)")
let followersRef = Database.database().reference().child("users/\(user.uid!)/followers/\(Auth.auth().currentUser!.uid)")
followingRef.observeSingleEvent(of: .value, with: { (snapshot) in
if !snapshot.exists() {
print("no following found")
followingRef.setValue("true") { (error, ref) in
if error != nil {
print(String(describing: error?.localizedDescription))
}
}
} else {
print("unfollowing")
snapshot.ref.removeValue()
}
})
followersRef.observeSingleEvent(of: .value, with: { (snapshot) in
if !snapshot.exists() {
print("no followers found")
followersRef.setValue("true") { (error, ref) in
if error != nil {
print(String(describing: error?.localizedDescription))
}
DispatchQueue.main.async {
self.followBarButtonItem.title = "Unfollow"
}
}
} else {
print("unfollowing")
snapshot.ref.removeValue()
DispatchQueue.main.async {
self.followBarButtonItem.title = "Follow"
}
}
})
}
Here's a picture of my tree: