Core Data not returning correct data sometimes - objective-c

Question

I have a custom object (Data) inheriting from NSObject, that needs to be persisted into core data. Hence I created a NSManagedObject (Transaction) that contains Data, something like this:
#interface Transaction (CoreDataProperties)
#property (nonatomic) BOOL m_isUploaded;
#property (nullable, nonatomic, retain) id m_transactionData; // this is the Data class, stored under Transformable
#property (nonatomic) int64_t m_submitDateTimeEpochMilliseconds;
#property (nullable, nonatomic, retain) NSString *m_uuid;
#end
I created one context and did everything related to the context on the main thread.
I made Data comply with NSCoding and NSCopying protocols. Also made some custom classes used in Data comply with NSCoding as well.
This is a short extract from Data.h:
#interface Data : NSObject <NSCoding, NSCopying>
#property (strong, nonatomic, nullable) HeldItem *m_heldItem;
#property (strong, nonatomic, nullable) NSDecimalNumber *m_discountAmount;
#property (strong, nonatomic, nonnull) NSMutableArray<Record *> *m_records;
#property (strong, nonatomic, nonnull) NSString *m_transactionId;
#property (nonatomic) CLLocationCoordinate2D m_location;
#property (strong, nonatomic, nullable) NSString *m_status;
- (void)encodeWithCoder:(nonnull NSCoder *)aCoder;
- (nonnull id)initWithCoder:(nonnull NSCoder *)aDecoder;
...lots of variables/methods here...
#end
If I purely just do insert, there are no issues (I confirmed this by looking at the variables during encodeWithCoder:). Or if I do purely just reading, there aren't no issues as well.
However, if I were to insert a new Transaction (and Data) record, and search/read an existing record and modify it (Data), the existing record doesn't get saved, and the new record is mostly blank (as if new). This issue happens at random. I could run it 8 times before I encounter this situation.
Any idea where I might have gone wrong? I've been stuck for quite some time.
This is the part where it seems to give me the problem:
// Store the existing/new data into Core Data
Transaction *t = [MANAGER createTransaction];
Data *data = [Data new];
t.m_kmsTransactionData = data;
// ...some assigning stuffs to other variables...
// ========== if this whole section is omitted the newly created record saves fine =========
Transaction *old = [MANAGER getTransactionFromCoreDataWithId:someOldDataIdString];
// oldData sometimes is returning a blank object (i.e. booleans are no, objects are nil etc)
Data *oldData = [old.m_kmsTransactionData mutableCopy];
oldData.m_status = #"old"; // testing to see if the old record gets updated
old.m_isUploaded = NO;
old.m_kmsTransactionData = [oldData copy];
// This doesn't work because oldData.m_transactionId is nil
data.m_transactionId = [MANAGER generateNewTransactionIDBasedOn:oldData.m_transactionId];
//===============================================
// ... more assigning code here ....
// Save context
[MANAGER saveDatabase];
-
// Some helper function in some manager
- (Transaction * _Nonnull)getTransactionFromCoreDataWithId:(NSString * _Nonnull)dataId
{
NSFetchRequest *request = [[NSFetchRequest alloc] initWithEntityName:[Transaction entityName]];
request.returnsObjectsAsFaults = NO;
NSError *error;
NSArray<Transaction *> *fetchedObjects = [self.m_coreDataStore.managedObjectContext executeFetchRequest:request error:&error];
NSAssert(fetchedObjects != nil, #"Failed to execute %#: %#", request, error);
if(fetchedObjects == nil || fetchedObjects.count == 0)
{
// error
return nil;
}
for(Transaction *t in fetchedObjects)
{
Data *td = t.m_kmsTransactionData;
if([td.m_salesRecordId isEqualToString:salesRecordId])
{
return t;
}
}
return nil;
}

Answer 1

I thought it was a Core Data quirk with transformable properties but it wasn't.
The part where I was
// ...some assigning stuffs to other variables...
I assigned m_salesRecordId to an existing id, which was already inside the database. So while searching through the getTransactionFromCoreDataWithId: method, it returned the newly created object based on the m_salesRecordId I've just made earlier.
As for why it worked sometimes and it didn't work sometimes was because the fetched query results wasn't sorted (I assume the order in which the results are returned are always not in sequence), so whichever record was returned first got returned as the searched object (which could either be the empty object I just created or the actual object that was already inside).
I still could not understand yet as to why even though the m_salesRecordId was nil after the screwup, the rest of the variables in the object could not be saved. But since everything is working as intended I'll take the win for now.
tl;dr:
Check your program logic again first