Error dealing with saveWithBlock and relation in MagicalRecord - ios

Question

I'm using MagicalRecord to change my custom CoreData functions with something better.
I have two entities: Offer (videogame offers) and System (consoles, PC, etx). An Offer can have one or many Systems, and I get all the data from a Parse query, where I save all my data.
I only have 8 Systems so when my app starts, I fetch all of them and save with Magical Record. Then I call my method to fetch some offers and transform the PFObjects from Parse into entities.
This is how
+ (void)createOrUpdateOffersWithArray:(NSArray *)objects completion:(void (^)())completion
{
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
for (PFObject *object in objects) {
Offer *offer = [Offer MR_findFirstByAttribute:#"offerId" withValue:object.objectId inContext:localContext];
if (offer == nil) {
offer = [Offer MR_createEntityInContext:localContext];
}
// Here I set all the offer values (title, date, etc)...
NSSet *offerSavedSystems = [offer mutableSetValueForKey:#"systems"];
if (offerSavedSystems == nil) {
offerSavedSystems = [[NSMutableSet alloc] init];
}
/* This is a set of all the systems related with the offer */
NSArray *offerSystems = [object objectForKey:#"sistemas"];
NSMutableSet *updatedSystems = [[NSMutableSet alloc] init];
/* Here I query one of my System entities for each in the "offerSystems" array */
for (NSString *systemKey in offerSystems) {
System *system = [System MR_findFirstByAttribute:#"key" withValue:systemKey inContext:localContext];
[updatedSystems addObject:system];
}
offer.systems = updatedSystems;
}
} completion:^(BOOL contextDidSave, NSError *error) {
/* UI update*/
}];
}
The weird this happens inside the last for loop. Despite I'm sure that all the 8 systems are inside my CoreData model, this line
System *system = [System MR_findFirstByAttribute:#"key" withValue:systemKey inContext:localContext];
returns nil
But the most weird thing is that using NSLOG just before the for loop like this
NSLog(#"SYSTEMS %d", [System MR_countOfEntities]);
NSLog(#"SYSTEMS WITH LOCAL CONTEXT %d", [System MR_countOfEntitiesWithContext:localContext]);
I got this
SYSTEMS 8
SYSTEMS WITH LOCAL CONTEXT 0
My Systems are previously saved with this method
+ (void)initializeSystems
{
NSArray *systemsKeys = [[self systems] allKeys];
for (NSString *systemKey in systemsKeys) {
System *system = [System MR_findFirstByAttribute:#"key" withValue:systemKey];
if (system == nil) {
system = [System MR_createEntity];
}
[MagicalRecord saveWithBlockAndWait:^(NSManagedObjectContext *localContext) {
system.key = systemKey;
system.name = [self literalForSystem:systemKey];
system.subscribed = [NSNumber numberWithBool:NO];
}];
}
}
What I'm doing wrong?
Thanks for your time

Answer 1

There are several possible problems with this line of code
System *system = [System MR_findFirstByAttribute:#"key" withValue:systemKey inContext:localContext];
systemKey value does not exist inside all of your entities.
system.key value not setted (or nil)
So, check firstly - fetch all system entities and log 'key' value. Insure that your key really exist.
Secondly,it's better to refactor your code for background saving
+ (void)initializeSystemsWithCompletion:(void (^)())completion
{
[MagicalRecord saveWithBlock:^(NSManagedObjectContext *localContext) {
NSArray *systemsKeys = [[self systems] allKeys];
for (NSString *systemKey in systemsKeys) {
System *system = [System MR_findFirstByAttribute:#"key" withValue:systemKey inContext:localContext];
if (system == nil) {
system = [System MR_createEntityInContext:localContext];
}
system.key = systemKey;
system.name = [self literalForSystem:systemKey];
system.subscribed = [NSNumber numberWithBool:NO];
}
} completion:^(BOOL success, NSError *error) {
}];
}