Firebase runTransactionBlock() deletes node - ios

Question

I am using Firebase SDK (2.4.2) for iOS. The following code is part of the didSelectPost() function used in SLComposeServiceViewController object. It's very important to indicate that this behavior is not the same when used in a regular UIViewController (weird I know).
Assuming the following basic code:
override func presentationAnimationDidFinish() {
// Retrieving content and identifying type here
}
override func didSelectPost() {
self.myRootRef.runTransactionBlock({
(currentData:FMutableData!) in
currentData.value = "test"
// Finalizing the transaction
return FTransactionResult.successWithValue(currentData)
}
)
self.extensionContext!.completeRequestReturningItems([], completionHandler: nil)
}
When the transaction is complete node_value disappears completely from Firebase. The value is not set and the node is deleted. This is a very weird and unexpected behavior!
On the other hand, the following code works as expected.
override func didSelectPost() {
self.myRootRef.setValue("test", withCompletionBlock: {
(error:NSError?, ref:Firebase!) in
if (error != nil) {
print("Data could not be saved.")
} else {
print("Data saved successfully!")
}
})
self.extensionContext!.completeRequestReturningItems([], completionHandler: nil)
}
This problem did not exist a couple of days ago, last I ran the code above. Any insights as to what the problem is?

Answer 1

If you set nil to a path in a Firebase database, it will do the same as a .removeValue().
When running a transaction you should check for nil. Since transactions can be called with nil if no default value was written.
myRootRef.runTransactionBlock({
(currentData:FMutableData!) in
var value = currentData.value as? Int
if value == nil {
value = 0
}
currentData.value = value! + 1
return FTransactionResult.successWithValue(currentData)
})
Read the Firebase Docs for more information.