Core Data is a framework for managing and persisting objects in iOS and macOS applications. It allows objects to be saved to and retrieved from persistent storage without having to write any of the data access code directly. Core Data includes entities to represent data, managed object contexts to work with entities, and a persistent store coordinator to coordinate saving to persistent stores like SQLite or custom stores. Entities are represented by managed objects that live within managed object contexts.

1. CORE DATA

2. WHAT IS CORE DATA?
•
data persistence framework
•
not a database

3. CORE DATA COMPONENTS
User application
Managed object context
Managed
object
Managed
object
Managed
object
Persistent store coordinator
Persistent store
(SQLite, XML,
in memory,
custom, …)
Managed
object
model

4. PERSISTENT STORE
•
NSPersistentStore
•
Types:
•
SQLite
•
Binary
•
In memory
•
Custom

5. PERSISTENT STORE
COORDINATOR
•
NSPersistentStoreCoordinator
•
associates persistent object stores and a managed
object model
•
facade to managed object contexts
•
group of persistent stores appears as a single
aggregate store

6. PERSISTENT STORE
COORDINATOR
•
Complex application
MOC
MOC
MOC
Persistent store coordinator
Storage1
Storage2
Storage3
Storage4

7. MANAGED OBJECT MODEL
(MOM)
•
A collection of entity descriptions
•
name of the class, properties (attributes and relationships)

8. MANAGED OBJECT CONTEXT
(MOC)
•
NSManagedObjectContext
•
environment where managed objects live
•
responsibility to manage a collection of managed objects
•
validation
•
faulting
•
(inverse) relationship handling
•
undo/redo
!
•
should be always accessible

9. MANAGED OBJECT
•
NSManagedObject
•
model object
•
represents a record from persistent store
Entity
description
Managed object - Person
dateOfBirth
07.03.1990.
firstName
Ivan
lastName
Horvat

10. CORE DATA PROJECT
•
INITIALISATION
•
•
managed object model
•
•
persistent store coordinator
managed object context
HOW?
•
use Xcode template

11. CORE DATA PROJECT
•
New project - Master-Detail Application

12. INSERTING OBJECT
NSManagedObjectContext *context = …
!
CDLocation *location = [NSEntityDescription
insertNewObjectForEntityForName:@“CDLocation”
inManagedObjectContext:context];
!
.
.
.
!
NSError *error = nil;
if (![context save:&error]) {
// Replace this implementation with code to handle the error appropriately.
NSLog(@“Error: %@“, error);
}

13. CONTEXT HIERARCHY
•
child - parent
MOC
MOC
MOC
MOC
MOC
MOC
MOC
MOC
Persistent store coordinator

14. TEMPORARY OBJECTS
•
!
child context:
NSManagedObjectContext *context = [[NSManagedObjectContext alloc]
initWithConcurrencyType:NSMainQueueConcurrencyType];
context.mergePolicy = NSMergeByPropertyObjectTrumpMergePolicy;
context.parentContext = self.managedObjectContext;
// self.managedObjectContext is main context
NSEntityDescription *entity = [[self.fetchedResultsController fetchRequest] entity];
NSManagedObject *newManagedObject = [NSEntityDescription
insertNewObjectForEntityForName:[entity name] inManagedObjectContext:context];
.
.
.

15. TEMPORARY OBJECTS
•
[context save:&error] will save object to main
context (parent context)
•
object is still not saved to persistent store
•
remove object from main context: undo or rollback
•
save object in persistent store: save main context

16. UNDO/REDO/ROLLBACK
•
NSUndoManager
[context setUndoManager:undoManager];
!
!
•
[context undo];
[context redo];
undo all unsaved changes
[context rollback];

17. FETCHING OBJECTS
•
NSFetchRequest
NSFetchRequest *request = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
entityForName:@“CDLocation"
inManagedObjectContext:context];
!
[request setEntity:entity];
NSArray *locations = [context executeFetchRequest:request
error:nil];

18. SORT RESULTS
•
NSSortDescriptor
NSFetchRequest *request = [[NSFetchRequest alloc] init];
…
…
…
NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc]
initWithKey: @"dateOfBirth" ascending:NO];
[request setSortDescriptors:@[sortDescriptor]];
!
NSArray *results = [context executeFetchRequest:request
error:nil];

19. FILTER RESULTS
•
NSPredicate
NSFetchRequest *request = [[NSFetchRequest alloc] init];
…
…
…
NSPredicate *predicate = [NSPredicate
predicateWithFormat:@"firstName contains %@", @"Ivana"];
[request setPredicate:predicate];
!
NSArray *results = [context executeFetchRequest:request
error:nil];

20. SEE ALSO
•
NSFetchedResultController
•
NSIncrementalStore
•
Custom storage types
•
Migrating data and versioning

21. LITERATURE
•
Apple documentation
Core Data programming Guide: https://developer.apple.com/library/mac/documentation/
cocoa/Conceptual/CoreData/cdProgrammingGuide.html
Core Data Core Competencies: https://developer.apple.com/library/ios/documentation/
DataManagement/Devpedia-CoreData/coreDataOverview.html
•
Pro Core Data for iOS - second edition
Michael Privat, Robert Warner