Receiving Subscription Update Events Before Uploader Has a Chance to Finish Uploading #12

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1. danieleggert commented on Mar 14, 2016

   

   danieleggert

   on Mar 14, 2016

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   Hi @timcamber — yes, that complicates things. We didn't anticipate this Cloud Kit behaviour.

   What does the Object Added Change Subscription look like? Is there anything in there that lets you know that the addition originates from that very same device?
2. timarnold commented on Mar 14, 2016

   

   timarnold

   on Mar 14, 2016

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   I'm not a Firebase expert, but I don't think there's inherently information about the origin of the objects coming from the remote destination. Of course we could add this --- I had not thought of adding something like a UDID to model objects. That might be the simplest way to solve this. The only other thing I had thought of was to have a separate object identifier (in fact, our app already has this, so it was a simple quick fix), and not to merge in objects from the subscription if the object already exists locally. I think using a UDID is a better fix.

   My subscription with Firebase is set up using their observeEventType(_: FEventType, withBlock: (FDataSnapshot) -> Void ) function, which simply sends an FDataSnapshot object to the closure whenever an update occurs. FDataSnapshot, as far as I can tell, doesn't tell me anything about how it came to be or where it came from.

   Edit: in case it's helpful, here is where I set up my subscription (Tasks instead of Moods, and I have tweaked the Remote protocol to accommodate this):

   func setupTaskSubscription(updateHandler: ([RemoteRecordChange<RemoteTask>]) -> Void) {
       tasksReference.observeEventType(.ChildAdded) { (snapshot: FDataSnapshot!) -> Void in
           if let contents = snapshot.value as? [String:AnyObject],
               let updatedTask = RemoteTask(record: FirebaseRecord(contents: contents, recordID: snapshot.key)) {
                   updateHandler([.Insert(updatedTask)])
           } else {
               updateHandler([])
           }
       }
   }
   

   which is invoked in, e.g., my TaskDownloader, like so:

   func setupForContext(context: ChangeProcessorContextType) {
       context.remote.setupTaskSubscription { (changes: [RemoteRecordChange<RemoteTask>]) -> Void in
           self.processChangedRemoteObjects(changes, context: context, completion: { _ in })
       }
   }
   

   Other than these changes, much of my implementation is the same as in your example.