merge changes to main context synchronously or asynchronously depending on the caller intention (fixes #65)

CoreStore/Internal/NSManagedObjectContext+Setup.swift

@@ -82,14 +82,28 @@ internal extension NSManagedObjectContext {
             object: rootContext,
             closure: { [weak context] (note) -> Void in
                 
-                context?.performBlock { () -> Void in
+                guard let rootContext = note.object as? NSManagedObjectContext,
+                    let context = context else {
+                        
+                        return
+                }
+                let mergeChanges = { () -> Void in
                     
                     let updatedObjects = (note.userInfo?[NSUpdatedObjectsKey] as? Set<NSManagedObject>) ?? []
                     for object in updatedObjects {
                         
-                        context?.objectWithID(object.objectID).willAccessValueForKey(nil)
+                        context.objectWithID(object.objectID).willAccessValueForKey(nil)
                     }
-                    context?.mergeChangesFromContextDidSaveNotification(note)
+                    context.mergeChangesFromContextDidSaveNotification(note)
+                }
+                
+                if rootContext.isSavingSynchronously == true {
+                    
+                    context.performBlockAndWait(mergeChanges)
+                }
+                else {
+                    
+                    context.performBlock(mergeChanges)
                 }
             }
         )

CoreStore/Internal/NSManagedObjectContext+Transaction.swift

@@ -55,6 +55,26 @@ internal extension NSManagedObjectContext {
         }
     }
     
+    internal var isSavingSynchronously: Bool? {
+        
+        get {
+            
+            let value: NSNumber? = getAssociatedObjectForKey(
+                &PropertyKeys.isSavingSynchronously,
+                inObject: self
+            )
+            return value?.boolValue
+        }
+        set {
+            
+            setAssociatedWeakObject(
+                newValue.flatMap { NSNumber(bool: $0) },
+                forKey: &PropertyKeys.isSavingSynchronously,
+                inObject: self
+            )
+        }
+    }
+    
     internal func isRunningInAllowedQueue() -> Bool {
         
         guard let parentTransaction = self.parentTransaction else {
@@ -89,7 +109,9 @@ internal extension NSManagedObjectContext {
             
             do {
                 
+                self.isSavingSynchronously = true
                 try self.save()
+                self.isSavingSynchronously = nil
             }
             catch {
                 
@@ -137,7 +159,9 @@ internal extension NSManagedObjectContext {
             
             do {
                 
+                self.isSavingSynchronously = false
                 try self.save()
+                self.isSavingSynchronously = nil
             }
             catch {
                 
@@ -185,5 +209,6 @@ internal extension NSManagedObjectContext {
     private struct PropertyKeys {
         
         static var parentTransaction: Void?
+        static var isSavingSynchronously: Void?
     }
 }