CoreData gets emptied after adding data into it - ios

Question

I have a CoreData entity Tracker which stores the dates.
The app receives a notification and the CheckListViewController enters data in CoreData for up to 13 days, so when the CheckListViewController gets dismissed, the CoreData entity Tracker will be filled with 13 rows.
In the MainViewController (which dismisses CheckListViewController), I have the following code:
- (void)dataSaved {
self.checkListVC dismissViewControllerAnimated:YES completion:^{
// fetching all the data from 'Tracker' entity and doing NSLog on it
// all data gets logged in console without any issues
}];
}
Now, after that somewhere in my code, I fetch all the data from the entity Tracker but the return data is empty. The CoreData doesn't show any error it simply returns and empty array.
Edit:
Code to fetch results from CoreData
NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:ENTITY];
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:#"date" ascending:NO];
[request setSortDescriptors:#[sortDescriptor]];
request.predicate = (fromDate && toDate) ? [NSPredicate predicateWithFormat:#"date >= %# AND date <= %#", fromDate, toDate] : nil;
__block NSArray* fetchedHabits;
[managedObjectContext performBlockAndWait:^{
NSError *error = nil;
fetchedHabits = [managedObjectContext executeFetchRequest:request error:&error];
if (error) NSLog(#"Unknown error occurred while fetching results from CoreData, %# : %#", error, [error userInfo]);
}];
CoreData model:
Update 1:
So as you can see there are two entities, namely Habit and Tracker. When I fetch results from Habit it all works fine, but when I try to fetch results from Tracker it gives me an empty array. I have a common NSManagedObjectContext instance because you can manage multiple CoreData entities with single managedObjectContext.
I have checked managedObjectContext.persistentStoreCoordinator.managedObjectModel.entitiesByName and it also lists both the entities.
Update 2:
Code where I add data in to Tracker
TrackerCoreData *tracker = [NSEntityDescription insertNewObjectForEntityForName:ENTITY
inManagedObjectContext:managedObjectContext];
tracker.date = date;
tracker.habits = habits;
// saving CoreData explicitly
NSError *error = nil;
[managedObjectContext save:&error];

Answer 1

There could be many reasons for your failure to display the records:
data was not saved
data was not retrieved correctly
data was not displayed correctly
All of these could be potentially complicated scenarios, but you should check them in this order.
A much better approach: use NSFetchedResultsController for your main view controller and have the delegate methods take care of updating your table view. No need to fetch, no work to be done in any completion methods - just save the data and the FRC will update your table.
Edit: how to check the physical database
It is possible that your data only exists in memory but is not actually saved to the database. Find the actual database file (in the documents folder of the app from the Simulator) and check it with the sqlite3 command line utility, or with the Firefox plugin "SQLite Manager".
Edit2: more concrete recommendations
You should make sure that you call:
[managedObjectContext save:&error];
Also double-check what your ENTITY macro stands for (not a very smart name).
It seems to me that you are overusing the block methods to no apparent purpose. First try to make everything work on the main thread (one context!). Only if you get performance problems consider background threads and context and calls to performBlock etc.