Cannot update NSManagedObject because of NSObjectInaccessible exception - ios

Question

I am building an app for displaying assets (PDF, Video, Etc).
It starts by downloading a JSON and parsing it into Core Data Objects <-- This part works fine.
These objects are a hierarchical set of Nodes that have a relationships set up in my model. each node can either be a FILE or a FOLDER. <-- no problems.
Then I have instance methods built into my NSManagedObject Subclasses that will download the file associated with that object (ie. a PDF). Then it sets
self.isAvailable = [NSNumber numberWithBool:YES];
Meanwhile, I have a UITableView that displays a list of assets. eventually it will update in real-time, but for now this is where I am having issue. I first had the view controller keep a pointer to the CoreData object that represents the folder it displays, but it appears that If the context gets updated, the pointer becomes invalid (ie. fails to fault).
Core data is not being very specific on what the problem is, or even where its happening, but it seems to crash when I set isAvailable with
*** Terminating app due to uncaught exception 'NSObjectInaccessibleException', reason: 'CoreData could not fulfill a fault for '0x1d5f9e50 <x-coredata://EDE66B97-B142-4E87-B445-76CAB965B676/Node/p58>''
I feel like the problem is that I shouldn't just keep a strong reference to a core data object as my model. Is there a better (less crashy) way to do this?
I have started playing with NSFetchedResultsController and using objectID's instead, but I haven't gotten anywhere yet.
- (void)populateChildren {
NSString * urlString = [NSString stringWithFormat:#"%#/%#", [CMPConstants hostURLString], self.SBUCode];
NSURL *url = [NSURL URLWithString:urlString];
NSURLRequest * request = [NSURLRequest requestWithURL:url];
[NSURLConnection sendAsynchronousRequest:request queue:self.downloadQueue completionHandler:^(NSURLResponse * response, NSData * data, NSError * error) {
if (data) {
NSDictionary * dict = [NSJSONSerialization JSONObjectWithData:data options:0 error:nil];
[self processParsedObject:dict];
} else {
NSLog(#"%#", urlString);
}
}];
}
#pragma mark - Parse JSON into NSManagedObjects
- (void)processParsedObject:(id)object {
[self processParsedObject:object depth:0 parent:nil key:nil];
[[NSManagedObjectContext MR_contextForCurrentThread] MR_saveToPersistentStoreAndWait];
}
- (void)processParsedObject:(id)object depth:(int)depth parent:(Node *)parent key:(NSString*)key {
if ([object isKindOfClass:[NSDictionary class]]) {
if (depth == 0) {
// Grab content node if depth is 0;
object = [object valueForKey:#"content"];
}
// FIXME: Change this to a real primary key once we get one.
static NSString * primaryKey = #"name";
// Look for existing object
Node * testNode = [Node MR_findFirstByAttribute:primaryKey withValue:[object valueForKey:primaryKey]];
// Create new node pointer
Node * newNode;
if (testNode) {
// Update existing Node
newNode = testNode;
} else {
// Build a new Node Object
newNode = [Node MR_createEntity];
newNode.isAvailable = [NSNumber numberWithBool:NO];
}
// Get keys
NSArray * keys = #[#"name",
#"type",
#"index",
#"size",
#"videoDemensions",
#"videoId",
#"fileName",
#"fileType",
#"path"];
if ([[object valueForKey:#"type"] isEqual:[NSNull null]]) {
NSLog(#"%#", object);
}
// Loop to set value for keys.
for (NSString * key in keys) {
id value = [object valueForKey:key];
if (![[object valueForKey:key] isKindOfClass:[NSNull class]]) {
[newNode setValue:value forKey:key];
}
}
// Set calculated properties.
[newNode setSbu:[self SBUCode]];
[newNode setParent:parent];
[[NSManagedObjectContext MR_contextForCurrentThread] MR_saveToPersistentStoreAndWait];
// Sync local file.
if (!newNode.isAvailable.boolValue) {
[newNode aquireFileInQueue:self.downloadQueue];
}
// Process children
for(NSString * newKey in [object allKeys]) {
id child = [object objectForKey:newKey];
[self processParsedObject:child depth:depth+1 parent:newNode key:newKey];
}
} else if ([object isKindOfClass:[NSArray class]]) {
for(id child in object) {
[self processParsedObject:child depth:depth+1 parent:parent key:nil];
}
} else {
// Nothing here, this processes each field.
}
}
This Method is an instance method of the Node class.
- (void)aquireFileInQueue:(NSOperationQueue *)queue {
if ([self.type isEqualToString:#"VIDEO"]) {
// Videos are available, but not downloaded.
self.isAvailableValue = YES;
return;
}
if (self.path == nil || self.fileName == nil) {
NSLog(#"Path or Filename for %# was nil", self.name);
return;
}
// Build the download URL !! MAKE SURE TO ADD PERCENT ESCAPES, this will protect against spaces in the file name
// Also make sure to slash-separate the path and fileName
NSURL * downloadURL = [NSURL URLWithString:[NSString stringWithFormat:#"%#/%#",
[self.path stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding],
[self.fileName stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding]]];
// Build the download request
NSURLRequest * downloadRequest = [NSURLRequest requestWithURL:downloadURL];
// FIXME: Authentication Code for JSON service
// Show network activity indicator
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:YES];
// Send Asynchronus Request for fileData
[NSURLConnection sendAsynchronousRequest:(NSURLRequest *)downloadRequest queue:queue completionHandler:^(NSURLResponse * response, NSData * data, NSError * error) {
// Hide network activity indicatior
[[UIApplication sharedApplication] setNetworkActivityIndicatorVisible:NO];
// Cast URL Response to HTTPURLResponse
NSHTTPURLResponse * httpResponse = (NSHTTPURLResponse *)response;
// If statusCode is 200 (successful) and data is not nil, save data
if (httpResponse.statusCode == 200 && data) {
[data writeToURL:[self fileURL] atomically:NO];
[[NSOperationQueue mainQueue] addOperationWithBlock:^{
[self setIsAvailable:[NSNumber numberWithBool:YES]];
}];
}
}];
}
- (void)prepareForDeletion {
// Remove file from Filesystem
[[NSFileManager defaultManager] removeItemAtURL:[self fileURL] error:nil];
}
- (NSURL *)fileURL {
// Return local file URL
return [NSURL fileURLWithPath:[NSString stringWithFormat:#"%#/%#", [Node applicationDocumentsDirectory], self.fileName]];
}

Answer 1

I am not familiar with MagicalRecords
A 'Could not fullfil fault' error occur when a context is holding an un-faulted object (an object stub), but the actual object in the database does not exist (deleted or was never saved).
My first advice:
If you work in a multithreaded environment, try to hold faulted objects.
use -existingObjectWithId:error: and fetch requests with:
[fetchRequest setReturnsObjectsAsFaults:NO];
[fetchRequest setIncludesPropertyValues:YES];
[fetchRequest setRelationshipKeyPathsForPrefetching:/*relationships you can afford to prefetch*/];
My second advice (to debug your issue):
Print you deletedObjects set before each save you make to the store to see which context caused the fault.
My third advice:
merge changes to the main context (my guess is that MagicalRecords does that for you).
note 1: deletes may be implied (you don't explicitly use deleteObject: by setting a relationship in cascade/deny mode for example)
note 2: you can not avoid this exception in a multithreaded environment (AFAIK), unless you pass all your saves through the main context (using parentContext) or by always using prefetched objects (not using relationships directly).