Firebase Child Added Is Called Every time a Child is Changed - ios

Question

I have a group messaging application that works fine until I want to change some of the basic group properties such as group title, image, etc. Before I show my code to display my conversations and update them I will show you some of my data structure.
When it comes to dealing with the displaying and editing of conversations I use two main nodes. An overall conversation node containing the conversation properties and a conversations node within my current user.
Here is what the conversation node in my current user looks like:
As you can see in the image above my user has a conversation node with a list of conversation ids. These conversation ids refer to a conversation node within my database. Here is a picture of the conversation node:
Just to review the problem. Basically when I update any of the conversation properties (title, image, members) it re calls my child added method which creates an error I will show later.
Here is my code to display the conversations:
func observeUserConversations() {
guard let uid = currentUserProperties.id else {
return
}
FIRDatabase.database().reference().child("users").child(uid).child("conversations").observe(.childAdded, with: { (snapshot) in
FIRDatabase.database().reference().child("conversations").child(snapshot.key).observe(.value, with: { (conversationSnapshot) in
if let conversation = Groups(snapshot: conversationSnapshot) {
conversation.groupId = conversationSnapshot.key
self.conversations.append(conversation)
DispatchQueue.main.async(execute: {
self.tableView.reloadData()
})
}
}, withCancel: nil)
}, withCancel: nil)
}
Here is my code to update some of the conversation properties:
static func updateConversationProperties(conversationId: String, property: String, propertyValue: String) {
let updateConversationPropertyRef = FIRDatabase.database().reference().child("conversations").child(conversationId).child(property)
updateConversationPropertyRef.setValue(propertyValue)
ProgressHUD.showSuccess("Field Updated!")
}
Please note I have tried using update child values instead of set value and it still has the same bug.
To sum up whenever I update a conversation property the child added function is called and appends a duplicate version of the conversation to my conversation array.
I know this may be a bit confusing, so I have a video here showing the bug:
https://youtu.be/OhhnYzQRKi8
In the video above you will see that the same conversaiton is duplicated and added twice.
Any help would be appreciated!
UPDATE
So I changed my observers a bit to look like this:
FIRDatabase.database().reference().child("users").child(uid).child("conversations").observe(.childAdded, with: { (snapshot) in
FIRDatabase.database().reference().child("conversations").child(snapshot.key).observeSingleEvent(of: .value, with: { (conversationSnapshot) in
if let conversation = Groups(snapshot: conversationSnapshot) {
conversation.groupId = conversationSnapshot.key
self.conversations.append(conversation)
DispatchQueue.main.async(execute: {
self.tableView.reloadData()
})
}
}, withCancel: nil)
}, withCancel: nil)
In the above code, everything works and no duplicates are made. However, now the conversations won't update in realtime. Instead they will display the old data and won't update to the newly changed data. Also if I add a conversation the new added conversaiton won't display.

Answer 1

Here is what I notice:
The way you had the code originally, the second listener was triggered any time a change is made to the value of /"conversations"/snapshot.key. And whenever this call was made, you were appending the conversationSnapshot to conversations array:
FIRDatabase.database().reference().child("users").child(uid).child("conversations").observe(.childAdded, with: { (snapshot) in
FIRDatabase.database().reference().child("conversations").child(snapshot.key).observe(of: .value, with: { (conversationSnapshot) in
if let conversation = Groups(snapshot: conversationSnapshot) {
conversation.groupId = conversationSnapshot.key
self.conversations.append(conversation) // here is where you are appending the data. This will be appended each time a change is made
DispatchQueue.main.async(execute: {
self.tableView.reloadData()
})
}
}, withCancel: nil)
}, withCancel: nil)
Now as you point out, if you change FIRDatabase.database().reference().child("conversations").child(snapshot.key).observe to .observeSingleEvent, the data won't append again, but you won't get updates. One option is whenever the listener is triggered, you search the array for the snapshot key, and then update the snapshot at that index if found. Not the most efficient method, to be sure.
In summation, it sounds like you do need to use observe, but as it stands, the data is duplicated because the code appends the snapshot to the end of the array whenever a change is made to the snapshot's value. You will have to use something other than self.conversations.append(conversation).
I'd be happy to brainstorm some other options if you wanted to message me directly.

Answer 2

FIRDatabase.database().reference().child("users").child(uid).child("conversations").observe(.childAdded, with: { (snapshot) in
FIRDatabase.database().reference().child("conversations").observe(.childAdded, with: { (conversationAdded) in
if conversationAdded.key == snapshot.key {
if let group = Groups(snapshot: conversationAdded) {
self.conversations.append(group)
DispatchQueue.main.async(execute: {
self.tableView.reloadData()
})
}
}
})
}, withCancel: nil)
FIRDatabase.database().reference().child("users").child(uid).child("conversations").observe(.childAdded, with: { (snapshot) in
FIRDatabase.database().reference().child("conversations").child(snapshot.key).observe(.childChanged, with: { (conversationSnapshot) in
let conversationIdsArray = self.conversations.map({$0.groupId})
let changeAtGroupIdIndex = conversationIdsArray.index(of: snapshot.key)
let conversationToBeUpdated = self.conversations[changeAtGroupIdIndex!]
conversationToBeUpdated.setValue(conversationSnapshot.value, forKeyPath: conversationSnapshot.key)
self.tableView.reloadData()
}, withCancel: nil)
}, withCancel: nil)
In the above code, I create two different observers. The first one loads conversations when the app is loaded or a conversation is added. The second one updates the conversation array if the child has been changed. This solves both problems.

Answer 3

Filter array with data excluding the object just received. Identify that object in the existing array by a unique id like groupID or chatID in my case. Then the repeated object will be removed
self.conversations = self.conversations.filter { obj in (obj.chatId as? String) != (data.chatId as? String) }
self.conversations.append(data)