Going Down the Core Data Rabbit Hole

Core Data is a great framework that Apple provides to help persist data in your applications. If you have familiarity with other persistence frameworks like N/Hibernate and Entity Framework then you may feel right at home with Core Data! Using SQLite directly can be a real pain, especially if you have little to no C experience. Core Data lets you ignore the actual store used and gives a great interface to make saving information a little more straightforward.

This session will cover the basics and intermediate topics of Core Data and some of the bigger gotchas that Apple's Documentation doesn't necessarily call out. I'll give some of the tips and tricks I've learned over the years of using Core Data so that you have less pain to get started. Core Data is certainly not the most friendly of APIs, but once you learn it, you'll use it all the time.

Transcript

1. Going Down the Core Data Rabbit Hole Aaron Douglas @astralbodies
2. Who am I? ✦ Aaron Douglas ✦ @astralbodies ✦ Automattic (WordPress) ✦ iOS Developer / Android (a little) ✦ Previous Life == Enterprise Java Developer
3. Who are you? ✦ iOS Developers? Tinkerers? ✦ Anyone use SQLite before? ✦ How about Core Data?
4. SQLite is GREAT ✦ Self-contained ✦ Server-less ✦ Nearly zero configuration ✦ Transactional ✦ Written in C / Super portable
5. SQLite meh ✦ Written in C ✦ No ARC ✦ Foundation wrappers ✦ Lots of boilerplate Code ✦ Room for archive/unarchive mapping errors
6. Why Core Data? ✦ Lets Step Back
7. ORM ✦ Object Relational Mapping ✦ Maps tables to real objects ✦ Persisting is relatively easy ✦ Less code (usually) ✦ Hibernate, Entity Framework, Ibatis
8. Why Core Data? ✦ In Appleland for many years - OS X Tiger, iPhone OS 3.0 ✦ Xcode visual designer ✦ Validation ✦ Migration ✦ Persist anywhere - SQLite, XML, memory
9. Core Data Topics ✦ Main moving parts ✦ Managed Object ✦ Managed Object Model & Context ✦ Persistent Store ✦ Persistent Store Coordinator ✦ Fetch Requests
10. Managed Objects
11. Models ✦ NSManagedObjectModel ✦ Designer in Xcode ✦ Through code
12. Managed Objects ✦ objectID ✦ NSString, NSDate, NSNumber ✦ Validation ✦ Undo Management ✦ Faults ✦ Refresh
13. Object Contexts ✦ Scratchpad ✦ Each object associated to single context ✦ Objects are not transferrable ✦ Nested contexts
14. Operations ✦ object = [NSManagedObject insertNewObjectForEntityForName:@”Speak er” inManagedObjectContext:context]; ✦ [context deleteObject:object];
15. Relationships ✦ NSSet ✦ NSOrderedSet ✦ Deletes
16. Finding Objects ✦ NSFetchRequest ✦ NSPredicate ✦ NSSortDescriptor
17. Fetching Example NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Appointment" inManagedObjectContext:context]; NSFetchRequest *request = [[NSFetchRequest alloc] init]; request.entity = entityDescription; NSPredicate *predicate1 = [NSPredicate predicateWithFormat:@"(date >= %@)", startDate]; NSPredicate *predicate2 = [NSPredicate predicateWithFormat:@"(date <= %@)", endDate]; NSPredicate *predicate3 = [NSPredicate predicateWithFormat:@"salesRep == %@", [self.salesRepService getSalesRepByGeneracId:salesRepId]]; NSPredicate *predicate4 = [NSPredicate predicateWithFormat:@"active == %@", @YES]; NSPredicate *predicate = [NSCompoundPredicate andPredicateWithSubpredicates:@[predicate1, predicate2, predicate3, predicate4]]; request.predicate = predicate; NSSortDescriptor *sortDescriptor1 = [NSSortDescriptor sortDescriptorWithKey:@"date" ascending:YES]; NSSortDescriptor *sortDescriptor2 = [NSSortDescriptor sortDescriptorWithKey:@"slotNumber" ascending:YES]; request.sortDescriptors = @[sortDescriptor1, sortDescriptor2]; ! NSArray *data = [context executeFetchRequest:request error:&error];
18. Fetching Example NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Appointment" inManagedObjectContext:context]; ! NSFetchRequest *request = [[NSFetchRequest alloc] init]; request.entity = entityDescription; ...
19. Fetching Example ... NSPredicate *predicate1 = [NSPredicate predicateWithFormat:@"(date >= %@)", startDate]; NSPredicate *predicate2 = [NSPredicate predicateWithFormat:@"(date <= %@)", endDate]; NSPredicate *predicate3 = [NSPredicate predicateWithFormat:@"salesRep == %@", salesRepId]; NSPredicate *predicate4 = [NSPredicate predicateWithFormat:@"active == %@", @YES]; NSPredicate *predicate = [NSCompoundPredicate andPredicateWithSubpredicates:@[predicate1, predicate2, predicate3, predicate4]]; ! request.predicate = predicate; ...
20. Fetching Example ... ! NSSortDescriptor *sortDescriptor1 = [NSSortDescriptor sortDescriptorWithKey:@"date" ascending:YES]; NSSortDescriptor *sortDescriptor2 = [NSSortDescriptor sortDescriptorWithKey:@"slotNumber" ascending:YES]; ! request.sortDescriptors = @[sortDescriptor1, sortDescriptor2]; ! ...
21. Fetching Example ... ! NSArray *data = [context executeFetchRequest:request error:&error]; ! ...
22. Performance ✦ NSFetchedResultsController ✦ Speeds up UITableView reloads & scrolling ✦ Watches for changes ✦ Reduces memory overhead
23. Persistent Stores
24. Persistent Stores ✦ NSPersistentStoreCoordinator ✦ Persisting, Loading, Caching Data ✦ Incremental Stores
25. Store Types ✦ NSPersistentStore ✦ XML (not on iOS) ✦ Atomic ✦ SQLite ✦ In-Memory
26. Validation
27. Core Data Validation ✦ Models have basic validation rules ✦ Single property validation ✦ Inter-property validation ✦ Multiple errors
28. Custom Validation ✦ validate<Key>:error: method in NSManagedObject subclass ✦ Do not call directly ✦ Common place for error codes/states
29. Inter-Property ✦ validateForInsert: validateForUpdate: overrides ✦ Make sure to call super ✦ Return NO if invalid; short-circuit if super is NO ✦ Easy to mess up!
30. Migration
31. Migrations ✦ Changing data models affect users new and existing ✦ Need a consistent state of data ✦ Defaults ✦ Field changes
32. Automatic Migration ✦ It’s MAGIC, right? ✦ Understand the issues
33. App Version Model Version 1.0 1 1.1 1 2.0 2 3.0 3
34. App Version Model Version 1.0 1 3.0 3 NSInferMappingModelAutomaticallyOption
35. Inferred Limitations ✦ Add & Remove Attributes ✦ Non-optional becomes optional ✦ Optional becomes non-optional with default ✦ Renaming entity or property
36. Manual Mapping ✦ More complex scenarios ✦ Code is needed for sequential migrations
37. Take-Aways ✦ Test migrations!! ✦ Keep old app binaries ✦ Pluck sqlite file for testing
38. Multi-Threading
39. Thread Confinement ✦ Separate MO Context for each thread ✦ Share Persistent Store Coordinator ✦ Pass object IDs rather than objects ✦ Track changes with notifications
40. Undo Manager
41. Undo Management ✦ NSUndoManager ✦ Built-in support in NSManagedObjectContext ✦ Undo manager is nil in iOS ✦ Simple to use, easy to mess up
42. Usage NSUndoManager *undoManager = [[NSUndoManager alloc] init]; ! undoManager.levelsOfUndo = 10; ! context.undoManager = undoManager; ! ... ! [context.undoManager undo];
43. Demo
44. References ✦ Core Data Programming Guide - Apple
 https://developer.apple.com/library/ios/ documentation/Cocoa/Conceptual/CoreData/ ✦ Core Data 2nd Ed - Marcus Zarra
45. Questions?