Advanced Core Data - Speaker Deck

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

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

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ADVANCED CORE DATA TOPICS • Concurrency • Caching Data • Migrating Schemas • Performance • Unit Testing

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ASK QUESTIONS This talk is all about you!

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

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CONCURRENCY “It’s so simple!”

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

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

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

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

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

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

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

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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

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CHALLENGES • Saving • Merging • Conﬂicts

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SAVING • NSManagedObjectContextDidSaveNotiﬁcation • Save in one spot • Handling problems

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

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

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DEMO Concurrency In Action

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CACHING DATA

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

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

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MIGRATING SCHEMAS

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

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

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AUTOMATIC MIGRATION • Infer Mapping Model • Migrate Store Automatically

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

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

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

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

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App Version Model Version 1.0 1 3.0 3 NSInferMappingModelAutomaticallyOption

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

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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

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

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PERFORMANCE

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

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

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

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

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TESTING

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XCTEST & CORE DATA • Unit testing code with Core Data is a pain • Managed Objects proliferate code • Test business logic, not necessarily Core Data

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WHAT DO I TEST? • Business logic • Integration with Core Data • Model Migrations • Concurrency • Timing / Performance

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DEMO Unit Testing Core Data

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IOS 8 CHANGES • NSBatchUpdateRequest • Cloud Kit • Under the hood

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QUESTIONS?

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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

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THANKS! Contact Information Aaron Douglas @astralbodies http://astralbodi.es