DRAFT: Fix: Do not save contexts if there are no any changes.

Code/CoreData/NSManagedObjectContext+RKAdditions.m

@@ -41,8 +41,6 @@ - (BOOL)saveToPersistentStore:(NSError **)error
     __block NSError *localError = nil;
     NSManagedObjectContext *contextToSave = self;
     while (contextToSave) {
-        __block BOOL success;
-
         /**
          To work around issues in ios 5 first obtain permanent object ids for any inserted objects.  If we don't do this then its easy to get an `NSObjectInaccessibleException`.  This happens when:
 
@@ -52,18 +50,27 @@ - (BOOL)saveToPersistentStore:(NSError **)error
          4. Save the child context to the parent context (the main one) which will work,
          5. Save the main context - a NSObjectInaccessibleException will occur and Core Data will either crash your app or lock it up (a semaphore is not correctly released on the first error so the next fetch request will block forever.
          */
-        __block BOOL obtained;
+        __block BOOL obtained = YES;
         [contextToSave performBlockAndWait:^{
-            obtained = [contextToSave obtainPermanentIDsForObjects:[[contextToSave insertedObjects] allObjects] error:&localError];
+            NSArray *objects = [[contextToSave insertedObjects] allObjects];
+            if (objects.count > 0) {
+                obtained =
+                [contextToSave obtainPermanentIDsForObjects:objects error:&localError];
+            }
         }];
         if (!obtained) {
             if (error) *error = localError;
             return NO;
         }
 
+        __block BOOL success = YES;
         [contextToSave performBlockAndWait:^{
-            success = [contextToSave save:&localError];
-            if (! success && localError == nil) RKLogWarning(@"Saving of managed object context failed, but a `nil` value for the `error` argument was returned. This typically indicates an invalid implementation of a key-value validation method exists within your model. This violation of the API contract may result in the save operation being mis-interpretted by callers that rely on the availability of the error.");
+            if ([contextToSave hasChanges]) {
+                success = [contextToSave save:&localError];
+                if (! success && localError == nil) {
+                    RKLogWarning(@"Saving of managed object context failed, but a `nil` value for the `error` argument was returned. This typically indicates an invalid implementation of a key-value validation method exists within your model. This violation of the API contract may result in the save operation being mis-interpretted by callers that rely on the availability of the error.");
+                }
+            }
         }];
 
         if (! success) {

Code/CoreData/RKManagedObjectImporter.m

@@ -275,10 +275,13 @@ - (BOOL)finishImporting:(NSError **)error
 
     __block BOOL success;
     __block NSError *localError = nil;
+    __weak typeof (self) weakSelf = self;
     [self.managedObjectContext performBlockAndWait:^{
-        success = [self.managedObjectContext save:&localError];
-        if (! success) {
-            RKLogCoreDataError(localError);
+        if ([weakSelf.managedObjectContext hasChanges]) {
+            success = [weakSelf.managedObjectContext save:&localError];
+            if (! success) {
+                RKLogCoreDataError(localError);
+            }
         }
     }];
 

Code/Network/RKManagedObjectRequestOperation.h

@@ -121,7 +121,13 @@
  @see `RKManagedObjectResponseMapperOperation`
  */
 @interface RKManagedObjectRequestOperation : RKObjectRequestOperation
-
+/**
+ If `true`, the CoreData context will be saved before making an API call.
+
+ Disabling context saving can help avoid potential app freezes, as the context is
+ saved synchronously on the thread from which it's called, including the main thread.
+ */
+@property (nonatomic, assign) BOOL shouldSaveContextBeforeAPICall;
 ///----------------------------------------
 /// @name Configuring Core Data Integration
 ///----------------------------------------

Code/Network/RKManagedObjectRequestOperation.m

@@ -473,6 +473,7 @@ - (instancetype)initWithHTTPRequestOperation:(RKHTTPRequestOperation *)requestOp
     self = [super initWithHTTPRequestOperation:requestOperation responseDescriptors:responseDescriptors];
     if (self) {
         self.savesToPersistentStore = YES;
+        self.shouldSaveContextBeforeAPICall = YES;
         self.deletesOrphanedObjects = YES;
         self.cachedResponse = [[NSURLCache sharedURLCache] cachedResponseForRequest:requestOperation.request];
     }
@@ -513,28 +514,29 @@ - (void)setManagedObjectContext:(NSManagedObjectContext *)managedObjectContext
     _managedObjectContext = managedObjectContext;
 
     if (managedObjectContext) {
-        [managedObjectContext performBlockAndWait:^{
-            if ([managedObjectContext hasChanges]) {
-                if ([managedObjectContext.insertedObjects count] && [self.managedObjectCache respondsToSelector:@selector(didCreateObject:)]) {
-                    for (NSManagedObject *managedObject in managedObjectContext.insertedObjects) {
-                        [self.managedObjectCache didCreateObject:managedObject];
+        if (self.shouldSaveContextBeforeAPICall) {
+            [managedObjectContext performBlockAndWait:^{
+                if ([managedObjectContext hasChanges]) {
+                    if ([managedObjectContext.insertedObjects count] && [self.managedObjectCache respondsToSelector:@selector(didCreateObject:)]) {
+                        for (NSManagedObject *managedObject in managedObjectContext.insertedObjects) {
+                            [self.managedObjectCache didCreateObject:managedObject];
+                        }
                     }
-                }
-
-                if ([managedObjectContext.updatedObjects count] && [self.managedObjectCache respondsToSelector:@selector(didFetchObject:)]) {
-                    for (NSManagedObject *managedObject in managedObjectContext.updatedObjects) {
-                        [self.managedObjectCache didFetchObject:managedObject];
+                    
+                    if ([managedObjectContext.updatedObjects count] && [self.managedObjectCache respondsToSelector:@selector(didFetchObject:)]) {
+                        for (NSManagedObject *managedObject in managedObjectContext.updatedObjects) {
+                            [self.managedObjectCache didFetchObject:managedObject];
+                        }
                     }
-                }
-
-                if ([managedObjectContext.deletedObjects count] && [self.managedObjectCache respondsToSelector:@selector(didDeleteObject:)]) {
-                    for (NSManagedObject *managedObject in managedObjectContext.deletedObjects) {
-                        [self.managedObjectCache didDeleteObject:managedObject];
+                    
+                    if ([managedObjectContext.deletedObjects count] && [self.managedObjectCache respondsToSelector:@selector(didDeleteObject:)]) {
+                        for (NSManagedObject *managedObject in managedObjectContext.deletedObjects) {
+                            [self.managedObjectCache didDeleteObject:managedObject];
+                        }
                     }
                 }
-            }
-        }];
-
+            }];
+        }
         // Create a private context
         NSManagedObjectContext *privateContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSPrivateQueueConcurrencyType];
         [privateContext setParentContext:managedObjectContext];
@@ -794,14 +796,18 @@ - (BOOL)saveContextToPersistentStore:(NSManagedObjectContext *)contextToSave fai
 {
     __block NSError *localError = nil;
     while (contextToSave) {
-        __block BOOL success;
+        __block BOOL success = YES;
         [contextToSave performBlockAndWait:^{
-            if (! [self isCancelled]) {
-                success = [contextToSave save:&localError];
-                if (! success && localError == nil) RKLogWarning(@"Saving of managed object context failed, but a `nil` value for the `error` argument was returned. This typically indicates an invalid implementation of a key-value validation method exists within your model. This violation of the API contract may result in the save operation being mis-interpretted by callers that rely on the availability of the error.");
-            } else {
-                // We have been cancelled while the save is in progress -- bail
-                success = NO;
+            if ([contextToSave hasChanges]) {
+                if (! [self isCancelled]) {
+                    success = [contextToSave save:&localError];
+                    if (! success && localError == nil) {
+                        RKLogWarning(@"Saving of managed object context failed, but a `nil` value for the `error` argument was returned. This typically indicates an invalid implementation of a key-value validation method exists within your model. This violation of the API contract may result in the save operation being mis-interpretted by callers that rely on the availability of the error.");
+                    }
+                } else {
+                    // We have been cancelled while the save is in progress -- bail
+                    success = NO;
+                }
             }
         }];
 
@@ -830,13 +836,20 @@ - (BOOL)saveContext:(NSManagedObjectContext *)context error:(NSError **)error
     if (self.savesToPersistentStore) {
         success = [self saveContextToPersistentStore:context failedContext:&failedContext error:&localError];
     } else {
-        [context performBlockAndWait:^{
-            success = ([self isCancelled]) ? NO : [context save:&localError];
-            if (!success) {
-                failedContext = context;
-            }
-        }];
+        if ([self isCancelled]) {
+            success = NO;
+        } else {
+            [context performBlockAndWait:^{
+                if ([context hasChanges]) {
+                    success = [context save:&localError];
+                    if (!success) {
+                        failedContext = context;
+                    }
+                }
+            }];
+        }
     }
+
     if (success) {
         if ([self.targetObject isKindOfClass:[NSManagedObject class]]) {
             [self.managedObjectContext performBlock:^{

Code/Network/RKObjectManager.h

@@ -484,7 +484,8 @@ RKMappingResult, RKRequestDescriptor, RKResponseDescriptor;
  */
 #ifdef RKCoreDataIncluded
 - (RKManagedObjectRequestOperation *)managedObjectRequestOperationWithRequest:(NSURLRequest *)request
-                                                         managedObjectContext:(NSManagedObjectContext *)managedObjectContext
+                                               shouldSaveContextBeforeAPICall:(BOOL)shouldSave
+                                                          managedObjectContext:(NSManagedObjectContext *)managedObjectContext
                                                                       success:(void (^)(RKObjectRequestOperation *operation, RKMappingResult *mappingResult))success
                                                                       failure:(void (^)(RKObjectRequestOperation *operation, NSError *error))failure;
 #endif

Code/Network/RKObjectManager.m

@@ -600,15 +600,22 @@ - (RKObjectRequestOperation *)objectRequestOperationWithRequest:(NSURLRequest *)
 
 #ifdef RKCoreDataIncluded
 - (RKManagedObjectRequestOperation *)managedObjectRequestOperationWithRequest:(NSURLRequest *)request
+                                               shouldSaveContextBeforeAPICall:(BOOL)shouldSave
                                                           managedObjectContext:(NSManagedObjectContext *)managedObjectContext
                                                                       success:(void (^)(RKObjectRequestOperation *operation, RKMappingResult *mappingResult))success
                                                                       failure:(void (^)(RKObjectRequestOperation *operation, NSError *error))failure
 {
-    return [self managedObjectRequestOperationWithRequest:request responseDescriptors:self.responseDescriptors managedObjectContext:managedObjectContext success:success failure:failure];
+    return [self managedObjectRequestOperationWithRequest:request
+                                      responseDescriptors:self.responseDescriptors
+                           shouldSaveContextBeforeAPICall:shouldSave
+                                     managedObjectContext:managedObjectContext
+                                                  success:success
+                                                  failure:failure];
 }
 
 - (RKManagedObjectRequestOperation *)managedObjectRequestOperationWithRequest:(NSURLRequest *)request
                                                           responseDescriptors:(NSArray *)responseDescriptors
+                                               shouldSaveContextBeforeAPICall:(BOOL)shouldSave
                                                          managedObjectContext:(NSManagedObjectContext *)managedObjectContext
                                                                       success:(void (^)(RKObjectRequestOperation *operation, RKMappingResult *mappingResult))success
                                                                       failure:(void (^)(RKObjectRequestOperation *operation, NSError *error))failure
@@ -619,6 +626,9 @@ - (RKManagedObjectRequestOperation *)managedObjectRequestOperationWithRequest:(N
     Class objectRequestOperationClass = [self requestOperationClassForRequest:request fromRegisteredClasses:self.registeredManagedObjectRequestOperationClasses] ?: [RKManagedObjectRequestOperation class];
     RKManagedObjectRequestOperation *operation = (RKManagedObjectRequestOperation *)[[objectRequestOperationClass alloc] initWithHTTPRequestOperation:HTTPRequestOperation responseDescriptors:responseDescriptors];
     [operation setCompletionBlockWithSuccess:success failure:failure];
+
+    operation.shouldSaveContextBeforeAPICall = shouldSave;
+
     operation.managedObjectContext = managedObjectContext ?: self.managedObjectStore.mainQueueManagedObjectContext;
     operation.managedObjectCache = self.managedObjectStore.managedObjectCache;
     operation.fetchRequestBlocks = self.fetchRequestBlocks;
@@ -659,7 +669,12 @@ - (id)appropriateObjectRequestOperationWithObject:(id)object
     if (isManagedObjectRequestOperation && self.managedObjectStore) {
         // Construct a Core Data operation
         NSManagedObjectContext *managedObjectContext = [object respondsToSelector:@selector(managedObjectContext)] ? [object managedObjectContext] : self.managedObjectStore.mainQueueManagedObjectContext;
-        operation = [self managedObjectRequestOperationWithRequest:request responseDescriptors:matchingDescriptors managedObjectContext:managedObjectContext success:nil failure:nil];
+        operation = [self managedObjectRequestOperationWithRequest:request
+                                               responseDescriptors:matchingDescriptors
+                                    shouldSaveContextBeforeAPICall:YES
+                                              managedObjectContext:managedObjectContext
+                                                           success:nil
+                                                           failure:nil];
 
         if ([object isKindOfClass:[NSManagedObject class]]) {
             static NSPredicate *temporaryObjectsPredicate = nil;