Two Steps Back

I’ve decided to break my blog down into four sections so that I cover the topics I intend to each week.  First will be “Progress” where I highlight the things I learned this week. Next will be “Reading” where I talk about what I am currently studying.  Following that will be “Quick Looks” where I talk about some technologies I briefly researched during the week.  Finally I will have “News” where I will talk about news that caught my eye this week.  So without further ado, here goes:

Progress

I didn’t make as much progress as I had hoped this week.  I did add Marcus Zarra’s CoreDataStack design to my project.  It was pretty straight forward.  Here is the initialization in Swift:

   init(dbName:String, syncToCloud:Bool, completion: ((Void) -> Void)? ) {  
     modelName = dbName  
     // Get the Model  
     let bundle = NSBundle.mainBundle()  
     let modelURL = bundle.URLForResource(dbName, withExtension: "momd")  
     let _model = NSManagedObjectModel(contentsOfURL: modelURL!)  
     assert(_model != nil, "Could not retrieve model at URL \(modelURL)")  
     model = _model!  
     // Build the persistent store coordinator  
     psc = NSPersistentStoreCoordinator(managedObjectModel: model)  
     // Set up the main MOC  
     mainQueueMOC = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)  
     // Create the private MOC, this is the parent context of the mainQueueMOC and it  
     // owns the persistent store.  
     privateMOC = NSManagedObjectContext(concurrencyType: .PrivateQueueConcurrencyType)  
     privateMOC.persistentStoreCoordinator = psc  
     // Make the main MOC a child of the private MOC  
     mainQueueMOC.parentContext = privateMOC  
     // Attach the basic life cycle listeners  
     attachInternalListeners()  
     dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {  
       // Get the proper options dictionary and storeURL based on the state  
       // of our sync flag.  
       var storeURL:NSURL?  
       var options:[NSObject: AnyObject]?  
       if (syncToCloud) {  
         storeURL = self.cloudStoreURL  
         if (self.rebuildFromCloudStore) {  
           options = self.cloudStoreOptionsWithRebuild  
         }  
         else {  
           options = self.cloudStoreOptions  
         }  
       }  
       else {  
         options = self.localStoreOptions  
         storeURL = self.localStoreURL  
       }  
       var error: NSError? = nil  
       self.store = self.psc.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: storeURL!, options: options!, error: &error)  
       assert(self.store != nil, "Could not add store URL \(storeURL)")  
       if let _completion = completion {  
         dispatch_async(dispatch_get_main_queue(),_completion)  
       }  
     }  
   }  

Where I got tripped up is in running the deduplication algorithm.  It worked but after migrating the store to iCloud then running the deduplication code and standing up a new NSFetchedResultsController I get the following error:

CoreData: Ubiquity:  Librarian returned a serious error for starting downloads Error Domain=BRCloudDocsErrorDomain Code=5 "The operation couldn’t be completed. (BRCloudDocsErrorDomain error 5 - No document at URL)"

Doing a few google searches I found that others are also seeing this error, but so far there is no answer.  I’m not sure this is really the error that is causing all the issues.  What I am seeing in my test app is if I include the deduplication code in the code path after the store is migrated (whether that be to the cloud or to local store) my app hangs right when I try to update the fetched results for my UITableView.  And yes, I am on the main queue when it happens so I know that is not the problem.

I’m also still running across folks giving up on CoreData and iCloud syncing so my decision to continue this investigation seems a little shakey.  I just wished I knew what they were moving to, since the problem of sync’d data seems like a required feature in today’s apps.  I do not want to stand up my own server to do this (although I am entirely capable of doing it) because I don’t want to incur the recurring cost for an app that might not be able to pay the server costs.

Reading

I am currently reading Spring in Action from Manning Publishing.  I’m about a third of the way through and it appears to be very thorough.  I need to work on a test app to apply what I am learning

News That Caught My Eye

Well the Apple Watch was opened for pre-order this past Friday.  I was up with the intent of buying one, but in the end I decided against it. At least for now.  I think I can get buy with the simulator as the supply chain gets filled and the first real users start reporting on it.

Quick Looks

I intended to look at React this past week, but ran out of cycles.  Maybe next week.