Advanced Core Data

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 unit testing.

Transcript

1. ADVANCED CORE DATA The Things You Thought You Could Ignore Much Wow.
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 • Performance • Unit Testing
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? • Stuttering / Instruments Core Data • 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 • Root/Master: Private Queue • UI: Main Queue as child of Master Context • Worker: Private Queue as child of Main Context • 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. DEMO Concurrency In Action
20. CACHING DATA
21. FETCHED RESULTS CONTROLLER • NSFetchedResultsController • Listens for context changes • Cache name & deleteCacheWithName:
22. BACKGROUND FETCHING • NSPersistentStoreCoordinator • Background fetch to warm up the cache
 request.resultType = NSManagedObjectIDResultType • Full fetch on background thread - NSPersistentStoreCoordinator caching
23. MIGRATING SCHEMAS
24. VERSIONING • Why use it? • Version number - hint • Hashes
25. ENTITY HASH • Name, Inheritance, Persistent properties • Class name, transient properties, user info, validation predicates, default values • Hash modifier
26. AUTOMATIC MIGRATION • Infer Mapping Model • Migrate Store Automatically
27. LIGHTWEIGHT MIGRATION • SQLite - all internal to db & no objects loaded into memory • Speedy • Light on memory
28. HEAVYWEIGHT MIGRATION • Every object loaded into memory • Manually map and manipulate data
29. INFER MAPPING MODEL • Not a silver bullet • Model upgrades can skip versions • Does not merge multiple versions • Business logic between upgrades is lost
30. App Version Model Version 1.0 1 1.1 1 2.0 2 3.0 3
31. App Version Model Version 1.0 1 3.0 3 NSInferMappingModelAutomaticallyOption
32. INFERRED LIMITATIONS • Add & Remove Attributes • Non-optional becomes optional • Optional becomes non-optional with default • Renaming entity or property
33. 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
34. TESTING • Test migrations LIKE CRAZY • Unit tests can help here! • Don’t assume current version only
35. PERFORMANCE
36. INSTRUMENTS • Run on the device • Fetches • Saves • Faults • Cache Misses
37. LOGGING • -com.apple.CoreData.SQLDebug 1 • Higher the number = more info • Loses usefulness pretty quick • Open SQLite file directly - Base.app
38. PREDICATES • contains • endsWith • like • matches • non-text first
39. MEMORY • Autorelease pools • NSManagedObjectContext reset • NSManagedObjectContext refreshObject:mergeChanges:
40. TESTING
41. XCTEST & CORE DATA • Unit testing code with Core Data is a pain • Managed Objects proliferate code • Test business logic, not necessarily Core Data
42. WHAT DO I TEST? • Business logic • Integration with Core Data • Model Migrations • Concurrency • Timing / Performance
43. DEMO Unit Testing Core Data
44. IOS 8 CHANGES • NSBatchUpdateRequest • Cloud Kit • Under the hood
45. QUESTIONS?
46. REFERENCES • Core Data Programming Guide - Apple
 This documentation is seriously out of date.
 No really.
 It’s bad. (better with iOS 8) • Core Data 2nd Ed - Marcus Zarra • RayWenderlich.com tutorials
47. THANKS! Contact Information Aaron Douglas @astralbodies http://astralbodi.es