So you've been using Core Data in your apps and think it's great and simple and super powerful. But now you're starting to run into problems with your apps that you can't explain and possibly even performance issues. This session will cover some of the more advanced topics about Core Data including doing things in the background (concurrency), caching data, migrating schemas, and dealing with undo management.

1. Much Wow.
ADVANCED CORE DATA
The Things You Thought You Could Ignore

2. WHO I AM
•
Aaron Douglas
•
Milwaukee, WI USA
•
Mobile Maker for
Automattic Inc.
(WordPress.com)
•
Prior life Enterprise Java
•
@astralbodies

3. ADVANCED CORE DATA
TOPICS
•
Concurrency
•
Caching Data
•
Migrating Schemas
•
Undo Management
•
Performance

4. ASK QUESTIONS
This talk is all about you!

5. CORE DATA IN 30 SECONDS
•
Object Graph Store
•
Abstracts Persistence
•
Provides a lot for doing a little
•
Validation, faulting, paging, querying, versioning

6. CONCURRENCY
“It’s so simple!”

7. MAIN THREAD
•
Easy
•
Pretty fast
•
Xcode wizard template
•
Good enough for most
apps & prototypes

8. WHEN DO I WORRY?
👉 Core Data 👎
•
Stuttering / Instruments
•
Asynchronous operations
•
Batch processing
•
Future-proofing app architecture

9. THREADING CAVEATS
•
NSManagedObjects belong to a single context
•
Do not share between threads/contexts
•
Pass by NSManagedObjectID
•
[[managedObject objectID] isTemporaryID]

10. IN THE BACKGROUND
•
Thread containment
•
Queues
•
Multiple contexts
•
Single persistent store coordinator

11. THREAD CONTAINMENT
•
Each thread gets its own
context
•
Manually manage contexts
•
Merge in changes from
NSManagedObjectContext
DidSaveNotification

12. QUEUES
•
NSManagedObjectContext initWithConcurrencyType:
•
NSMainQueueConcurrencyType
•
NSPrivateQueueConcurrencyType
•
NSConfinementConcurrencyType
•
Parent context
•
NSManagedObjectContextDidSaveNotification

13. QUEUES
•
performBlock - immediately returns
•
performWithBlockAndWait
•
Main thread can still execute directly

14. PREFERRED SETUP
•
Primary: Private Queue
•
UI: Main Queue as child of
Primary
•
Background: Private Queue
as child of Primary
•
Allows for asynchronous
saves
http://floriankugler.com/blog/2013/4/2/the-concurrent-core-data-stack

15. CHALLENGES
•
Saving
•
Merging
•
Conflicts

16. SAVING
•
NSManagedObjectContextDidSaveNotification
•
Save in one spot
•
Handling problems

17. MERGING
•
NSMergePolicy
•
NSErrorMergePolicy - default
•
NSMergeByPropertyStoreTrumpMergePolicy
•
NSMergeByPropertyObjectTrumpMergePolicy
•
NSOverwriteMergePolicy

18. CONFLICTS
•
NSErrorMergePolicy
•
NSError
userInfo[@“conflictList”]
•
User probably needs to
decide
•
UX is key!

19. CACHING
DATA

20. FETCHED RESULTS
CONTROLLER
•
NSFetchedResultsController
•
Listens for context changes
•
Cache name & deleteCacheWithName:

21. BACKGROUND FETCHING
•
NSPersistentStoreCoordinator
•
Background fetch to warm up the cache
request.resultType =
NSManagedObjectIDResultType
•
Full fetch on background thread NSPersistentStoreCoordinator caching

22. MIGRATING
SCHEMAS

23. VERSIONING
•
Why use it?
•
Version number - hint
•
Hashes

24. ENTITY HASH
•
Name, Inheritance, Persistent properties
•
Class name, transient properties, user info,
validation predicates, default values
•
Hash modifier

25. AUTOMATIC MIGRATION
•
Infer Mapping Model
•
Migrate Store Automatically

26. LIGHTWEIGHT MIGRATION
•
SQLite - all internal to db & no objects loaded
into memory
•
Speedy
•
Light on memory

27. HEAVYWEIGHT MIGRATION
•
Every object loaded into memory
•
Manually map and manipulate data

28. INFER MAPPING MODEL
•
Not a silver bullet
•
Model upgrades can skip versions
•
Does not merge multiple versions
•
Business logic between upgrades is lost

29. App
Version
1.0
1.1
2.0
3.0
1
1
2
3
Model
Version

30. App
Version
1.0
3.0
Model
Version
1
3
NSInferMappingModelAutomaticallyOption

31. INFERRED LIMITATIONS
•
Add & Remove Attributes
•
Non-optional becomes optional
•
Optional becomes non-optional with default
•
Renaming entity or property

32. MANUAL MAPPING
•
More complex scenarios
•
Mapping model is for specific version to version
•
Multiple version change not support unless
sequential migrations used
•
Code is needed for sequential migrations

33. TESTING
•
Test migrations LIKE CRAZY
•
Unit tests can help here!
•
Don’t assume current version only

34. UNDO
MANAGEMENT

35. UNDO MANAGEMENT
•
NSUndoManager
•
Built-in support in NSManagedObjectContext
•
Undo manager is nil in iOS
•
Simple to use, easy to mess up

36. Usage
NSUndoManager *undoManager =
[[NSUndoManager alloc] init];
!
undoManager.levelsOfUndo = 10;
!
context.undoManager = undoManager;
!
...
!
[context.undoManager undo];

37. PERFORMANCE

38. INSTRUMENTS
•
Run on the device
•
Fetches
•
Saves
•
Faults
•
Cache Misses

39. LOGGING
•
-com.apple.CoreData.SQLDebug 1
•
Higher the number = more info
•
Loses usefulness pretty quick
•
Open SQLite file directly - Base.app

40. PREDICATES
•
contains
•
endsWith
•
like
•
matches
•
non-text first

41. MEMORY
•
Autorelease pools
•
NSManagedObjectContext reset
•
NSManagedObjectContext
refreshObject:mergeChanges:

42. QUESTIONS?

43. REFERENCES
•
Core Data Programming Guide - Apple
This documentation is seriously out of date.
No really.
It’s bad.
•
Core Data 2nd Ed - Marcus Zarra

44. THANKS!
Contact Information
Aaron Douglas
@astralbodies
http://github.com/astralbodies