Magical Record detect no changes in default context - ios

Question

I am using Magical Record for my app so I can make use of their core data stack that should automatically propagate my changes in my worker context (core data thread) to the default context (of the main thread). I have been creating and updating my objects in a core data write queue and everything was working fine.
Then I ran into this issue that Magical Record was able to save my changes on my worker context, but when it tries to save to the default context, it detects no changes and therefore doesn't save.
Where did I do wrong? In the rest of my app, I am creating and updating in pretty much the same way and it works. Please help. Thank you!
Below is the related code:
Where no changes were detected after all these changes:
dispatch_async(CoreDataWriteQueue(), ^{
if (self.person) {
FTPerson *localPerson = [FTPerson fetchWithID:self.person.id];
[localPerson setName:self.nameField.text];
[localPerson trainWithImages:self.addedImages];
} else {
FTPerson *newPerson = [[FTPerson alloc] initWithName:self.nameField.text andInitialTrainingImages:self.addedImages];
FTGroup *localGroup = [FTGroup fetchWithID:self.group.id];
[newPerson addGroup:localGroup];
}
[[NSManagedObjectContext MR_contextForCurrentThread] MR_saveToPersistentStoreAndWait];
});
I have also tried the saveWithBlock method and no luck:
dispatch_async(CoreDataWriteQueue(), ^{
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext){
if (self.person) {
FTPerson *localPerson = [FTPerson fetchWithID:self.person.id];
[localPerson setName:self.nameField.text];
[localPerson trainWithImages:self.addedImages];
} else {
FTPerson *newPerson = [[FTPerson alloc] initWithName:self.nameField.text andInitialTrainingImages:self.addedImages];
FTGroup *localGroup = [FTGroup fetchWithID:self.group.id];
[newPerson addGroup:localGroup];
}
}];
});
And here is where I created the person and group objects:
dispatch_async(CoreDataWriteQueue(), ^{
FTPerson *newPerson = [[FTPerson alloc] initWithName:#"test" andInitialTrainingImages:#[[UIImage imageNamed:#"test.jpg"]]];
});
dispatch_async(CoreDataWriteQueue(), ^{
FTGroup *newGroup = [[FTGroup alloc] init];
[self setGroup:newGroup];
});
Also the init methods:
Person
- (id)initWithName:(NSString *)name andInitialTrainingImages:(NSArray *)images {
NSManagedObjectContext *context = [NSManagedObjectContext MR_contextForCurrentThread];
self = [FTPerson MR_createInContext:context];
self.name = name;
self.id = [[NSUUID UUID] UUIDString];
self.objectIDString = [[self.objectID URIRepresentation] absoluteString];
self.trainingImages = [[NSMutableArray alloc] init];
[context MR_saveToPersistentStoreAndWait];
return self;
}
Group
- (id)init {
NSManagedObjectContext *context = [NSManagedObjectContext MR_contextForCurrentThread];
self = [FTGroup MR_createInContext:context];
self.id = [[NSUUID UUID] UUIDString];
self.didFinishTraining = NO;
self.didFinishProcessing = NO;
self.photosTrained = #(0);
self.lastProcessedDate = [NSDate date];
[context MR_saveToPersistentStoreAndWait];
return self;
}
FIXED
So the problem ended up being unrelated to magical record.
I was adding objects to my core data NSSet incorrectly. Instead of making it a NSMutableSet and do addObject:, I should have:
NSMutableSet *mutablePhotos = [self mutableSetValueForKey:#"photos"];
[mutablePhotos addObject:photo];

Answer 1

So the problem ended up being unrelated to magical record. I was adding objects to my core data NSSet incorrectly. Instead of making it a NSMutableSet and do addObject:, I should have:
NSMutableSet *mutablePhotos = [self mutableSetValueForKey:#"photos"];
[mutablePhotos addObject:photo];

Answer 2

I don't think you should be using your own dispatch queues when dealing with Core Data. The whole point of the -performBlock: methods on NSManagedObjectContext is that Core Data takes care of executing the provided block on the correct queue.
Now to answer your question. First, are you using MagicalRecord 2.x or 3.0? If 2.x, please make sure you use the develop branch, or alternatively grab the latest release (v2.3beta5 at this time). There are a lot of improvements in the latest dev and release branches.
Second, I think it is important when multithreading with Core Data to do two things:
Always turn on concurrency debugging by editing your scheme and setting -com.apple.CoreData.ConcurrencyDebug 1
Always be very explicit as to which context you mean to use. There is a reason that the method -MR_contextForCurrentThread is no longer recommended by the MagicalRecord team. Modify your create methods to take an NSManagedObjectContext as a parameter so there is never a doubt as to what context is creating it.
Try making the following changes:
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext){
if (self.person) {
FTPerson *localPerson = [self.person MR_inContext:localContext];
[localPerson setName:self.nameField.text];
[localPerson trainWithImages:self.addedImages];
} else {
FTPerson *newPerson = [[FTPerson alloc] initWithName:self.nameField.text andInitialTrainingImages:self.addedImages inContext:localContext];
FTGroup *localGroup = [self.group MR_inContext:localContext];
[newPerson addGroup:localGroup];
}
}];
Person:
- (id)initWithName:(NSString *)name andInitialTrainingImages:(NSArray *)images inContext:(NSManagedObjectContext*)context {
self = [FTPerson MR_createInContext:context];
self.name = name;
self.id = [[NSUUID UUID] UUIDString];
self.objectIDString = [[self.objectID URIRepresentation] absoluteString];
self.trainingImages = [[NSMutableArray alloc] init];
[context MR_saveToPersistentStoreAndWait];
return self;
}
For Person, I notice you pass in an array of images but you assign an empty array to the new person entity. Do you mean to do that?
Group:
-(id)initWithContext:(NSManagedObjectContext*)context {
self = [FTGroup MR_createInContext:context];
self.id = [[NSUUID UUID] UUIDString];
self.didFinishTraining = NO;
self.didFinishProcessing = NO;
self.photosTrained = #(0);
self.lastProcessedDate = [NSDate date];
[context MR_saveToPersistentStoreAndWait];
return self;
}