re-work stack structure (#72). close #60

- Change CoreDataStack returned by Factory
- mainContext is now directly connected to the persistent store
coordinator instead of being a child of the background context.
- Update CoreDataStack to reflect new stack setup
- Changes are merged between background and main contexts using
`mergeChangesFromContextDidSaveNotification(_:)`

Source/CoreDataStack.swift

@@ -26,11 +26,11 @@ import Foundation
 
  It is composed of a main context and a background context.
  These two contexts operate on the main queue and a private background queue, respectively.
- The background context is the root level context, which is connected to the persistent store coordinator.
- The main context is a child of the background context.
+ Both are connected to the persistent store coordinator.
 
- Data between these two primary contexts and child contexts is kept in sync.
- Changes to a context are propagated to its parent context and eventually the persistent store when saving.
+ Data between the main and background contexts is perpetually kept in sync.
+
+ Changes to a child context are propagated to its parent context and eventually the persistent store when saving.
 
  - warning: **You cannot create a `CoreDataStack` instance directly. Instead, use a `CoreDataStackFactory` for initialization.**
  */
@@ -72,10 +72,15 @@ public final class CoreDataStack: CustomStringConvertible, Equatable {
         self.backgroundContext = backgroundContext
         self.storeCoordinator = storeCoordinator
 
-        NSNotificationCenter.defaultCenter().addObserver(self,
-                                                         selector: #selector(didReceiveChildContextDidSaveNotification(_:)),
-                                                         name: NSManagedObjectContextDidSaveNotification,
-                                                         object: mainContext)
+        let notificationCenter = NSNotificationCenter.defaultCenter()
+        notificationCenter.addObserver(self,
+                                       selector: #selector(didReceiveMainContextDidSaveNotification(_:)),
+                                       name: NSManagedObjectContextDidSaveNotification,
+                                       object: mainContext)
+        notificationCenter.addObserver(self,
+                                       selector: #selector(didReceiveBackgroundContextDidSaveNotification(_:)),
+                                       name: NSManagedObjectContextDidSaveNotification,
+                                       object: backgroundContext)
     }
 
     /// :nodoc:
@@ -144,5 +149,14 @@ public final class CoreDataStack: CustomStringConvertible, Equatable {
 
         saveContext(parentContext)
     }
-
+
+    @objc
+    private func didReceiveBackgroundContextDidSaveNotification(notification: NSNotification) {
+        mainContext.mergeChangesFromContextDidSaveNotification(notification)
+    }
+
+    @objc
+    private func didReceiveMainContextDidSaveNotification(notification: NSNotification) {
+        backgroundContext.mergeChangesFromContextDidSaveNotification(notification)
+    }
 }

Source/CoreDataStackFactory.swift

@@ -92,7 +92,7 @@ public struct CoreDataStackFactory: CustomStringConvertible, Equatable {
 
             dispatch_async(dispatch_get_main_queue()) {
                 let mainContext = self.createContext(.MainQueueConcurrencyType, name: "main")
-                mainContext.parentContext = backgroundContext
+                mainContext.persistentStoreCoordinator = storeCoordinator
 
                 let stack = CoreDataStack(
                     model: self.model,
@@ -128,7 +128,7 @@ public struct CoreDataStackFactory: CustomStringConvertible, Equatable {
         backgroundContext.persistentStoreCoordinator = storeCoordinator
 
         let mainContext = self.createContext(.MainQueueConcurrencyType, name: "main")
-        mainContext.parentContext = backgroundContext
+        mainContext.persistentStoreCoordinator = storeCoordinator
 
         let stack = CoreDataStack(
             model: model,

Tests/ContextSyncTests.swift

@@ -50,7 +50,6 @@ class ContextSyncTests: TestCase {
 
         // WHEN: we save the main context
         expectationForNotification(NSManagedObjectContextDidSaveNotification, object: inMemoryStack.mainContext, handler: nil)
-        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: inMemoryStack.backgroundContext, handler: nil)
 
         saveContext(inMemoryStack.mainContext) { result in
             XCTAssertTrue(result == .success)
@@ -76,6 +75,17 @@ class ContextSyncTests: TestCase {
         let companies = generateDataInContext(inMemoryStack.backgroundContext, companiesCount: 3, employeesCount: 3)
         let companyNames = companies.map { $0.name }
 
+        // WHEN: we save the background context
+        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: inMemoryStack.backgroundContext, handler: nil)
+
+        saveContext(inMemoryStack.backgroundContext) { result in
+            XCTAssertTrue(result == .success)
+        }
+
+        waitForExpectationsWithTimeout(DefaultTimeout) { (error) in
+            XCTAssertNil(error, "Expectation should not error")
+        }
+
         // WHEN: we fetch the objects from the main context
         let request = FetchRequest<Company>(entity: entity(name: Company.entityName, context: inMemoryStack.mainContext))
         let results = try! fetch(request: request, inContext: inMemoryStack.mainContext)

Tests/SaveTests.swift

@@ -54,9 +54,9 @@ class SaveTests: TestCase {
             return true
         }
 
-        var didSaveBackground = false
-        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: stack.backgroundContext) { (notification) -> Bool in
-            didSaveBackground = true
+        var didUpdateBackground = false
+        expectationForNotification(NSManagedObjectContextObjectsDidChangeNotification, object: stack.backgroundContext) { (notification) -> Bool in
+            didUpdateBackground = true
             return true
         }
 
@@ -74,7 +74,7 @@ class SaveTests: TestCase {
         waitForExpectationsWithTimeout(DefaultTimeout, handler: { (error) -> Void in
             XCTAssertNil(error, "Expectation should not error")
             XCTAssertTrue(didSaveMain, "Main context should be saved")
-            XCTAssertTrue(didSaveBackground, "Background context should be saved")
+            XCTAssertTrue(didUpdateBackground, "Background context should be updated")
         })
     }
 
@@ -90,9 +90,9 @@ class SaveTests: TestCase {
             return true
         }
 
-        var didSaveBackground = false
-        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: stack.backgroundContext) { (notification) -> Bool in
-            didSaveBackground = true
+        var didUpdateBackground = false
+        expectationForNotification(NSManagedObjectContextObjectsDidChangeNotification, object: stack.backgroundContext) { (notification) -> Bool in
+            didUpdateBackground = true
             return true
         }
 
@@ -105,7 +105,7 @@ class SaveTests: TestCase {
         waitForExpectationsWithTimeout(DefaultTimeout, handler: { (error) -> Void in
             XCTAssertNil(error, "Expectation should not error")
             XCTAssertTrue(didSaveMain, "Main context should be saved")
-            XCTAssertTrue(didSaveBackground, "Background context should be saved")
+            XCTAssertTrue(didUpdateBackground, "Background context should be updated")
         })
     }
 
@@ -135,9 +135,9 @@ class SaveTests: TestCase {
             return true
         }
 
-        var didSaveBackground = false
-        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: stack.backgroundContext) { (notification) -> Bool in
-            didSaveBackground = true
+        var didUpdateBackground = false
+        expectationForNotification(NSManagedObjectContextObjectsDidChangeNotification, object: stack.backgroundContext) { (notification) -> Bool in
+            didUpdateBackground = true
             return true
         }
 
@@ -155,7 +155,7 @@ class SaveTests: TestCase {
         waitForExpectationsWithTimeout(DefaultTimeout, handler: { (error) -> Void in
             XCTAssertNil(error, "Expectation should not error")
             XCTAssertTrue(didSaveMain, "Main context should be saved")
-            XCTAssertTrue(didSaveBackground, "Background context should be saved")
+            XCTAssertTrue(didUpdateBackground, "Background context should be updated")
         })
     }
 
@@ -178,9 +178,9 @@ class SaveTests: TestCase {
             return true
         }
 
-        var didSaveBackground = false
-        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: stack.backgroundContext) { (notification) -> Bool in
-            didSaveBackground = true
+        var didUpdateBackground = false
+        expectationForNotification(NSManagedObjectContextObjectsDidChangeNotification, object: stack.backgroundContext) { (notification) -> Bool in
+            didUpdateBackground = true
             return true
         }
 
@@ -199,7 +199,43 @@ class SaveTests: TestCase {
             XCTAssertNil(error, "Expectation should not error")
             XCTAssertTrue(didSaveChild, "Child context should be saved")
             XCTAssertTrue(didSaveMain, "Main context should be saved")
+            XCTAssertTrue(didUpdateBackground, "Background context should be updated")
+        })
+    }
+
+    func test_ThatSavingBackgroundContext_SucceedsAndUpdateMainContext() {
+        // GIVEN: a stack and context with changes
+        let stack = self.inMemoryStack
+
+        generateCompaniesInContext(stack.backgroundContext, count: 3)
+
+        var didSaveBackground = false
+        expectationForNotification(NSManagedObjectContextDidSaveNotification, object: stack.backgroundContext) { (notification) -> Bool in
+            didSaveBackground = true
+            return true
+        }
+
+        var didUpdateMain = false
+        expectationForNotification(NSManagedObjectContextObjectsDidChangeNotification, object: stack.mainContext) { (notification) -> Bool in
+            didUpdateMain = true
+            return true
+        }
+
+        let saveExpectation = expectationWithDescription("\(#function)")
+
+        // WHEN: we attempt to save the context asynchronously
+        saveContext(stack.backgroundContext, wait: false) { result in
+
+            // THEN: the save succeeds without an error
+            XCTAssertTrue(result == .success, "Save should not error")
+            saveExpectation.fulfill()
+        }
+
+        // THEN: then the main and background contexts are saved and the completion handler is called
+        waitForExpectationsWithTimeout(DefaultTimeout, handler: { (error) -> Void in
+            XCTAssertNil(error, "Expectation should not error")
             XCTAssertTrue(didSaveBackground, "Background context should be saved")
+            XCTAssertTrue(didUpdateMain, "Main context should be updated")
         })
     }
 

Tests/StackFactoryTests.swift

@@ -126,7 +126,7 @@ class StackFactoryTests: TestCase {
 
         XCTAssertEqual(stack.mainContext.name, "JSQCoreDataKit.CoreDataStack.context.main")
         XCTAssertEqual(stack.mainContext.concurrencyType, NSManagedObjectContextConcurrencyType.MainQueueConcurrencyType)
-        XCTAssertEqual(stack.mainContext.parentContext, stack.backgroundContext)
+        XCTAssertNil(stack.mainContext.parentContext)
         XCTAssertNotNil(stack.mainContext.persistentStoreCoordinator)
 
         XCTAssertEqual(stack.backgroundContext.name, "JSQCoreDataKit.CoreDataStack.context.background")