Core Data

Core Data can be intimidating at first. With a proper introduction, the transition into using Core Data can be much smoother. This presentation gives an overview of the core and advanced parts of Core Data.

1. Core Data By Robert Brown @robby_brown
2. Basic Core Data
3. What is Core Data? Intimidating An amazing data persistence framework Not a database
4. Model View Controller Model Controller View Interface Builder Core Data Xcode
5. Core Data Layers XML SQLite Binary In Memory Custom NSPersistentStore NSPersistentStoreCoordinator NSManagedObjectModel NSManagedObjectContext NSManagedObject Application NSManagedObject Subclass
6. Persistent Store NSPersistentStore Four storage types: XML (Mac only), SQLite, binary, and in memory Developers can add their own custom formats
7. Persistent Store Coordinator NSPersistentStoreCoordinator Façade between persistent store(s) and managed object context(s) May only have one MOM Not thread safe! lock, unlock, and tryLock methods are provided.
8. Persistent Store Coordinator Persistent Store Coordinator Managed Object Contexts Persistent Stores
9. Managed Object Model NSManagedObjectModel A representation of the app’s data model Visually built in Xcode (usually) Commonly called a “MOM”
10. Managed Object Model
11. Entities NSEntityDescription Entities represent objects Entities can have attributes such as numbers and strings Entities can have to-one and to-many relationships to other entities
12. Managed Object Context NSManagedObjectContext The “scratch pad” of you application Changes aren’t saved until calling save: Always check for errors Create a new context for each thread Commonly called a “MOC”
13. Managed Object NSManagedObject Superclass of all managed objects Properties can be accessed via KVC/KVO Don’t pass managed objects between threads, pass their objectID instead
14. Fetch Requests NSFetchRequest Used to retrieve objects from the store Uses an NSPredicate for the query
15. Advanced Core Data
16. Fetch Request Efficiency Smaller batches may be requested for greater efficiency (SQLite only) Objects may be returned as faults SUBQUERY can be used to have the database do the work instead of Core Data Jedi Level
17. Fetch Request Templates Common fetch requests can be stored as a template For example, all persons with a given name Use fetchRequestFromTemplateWithName: substitutionVariables: Jedi Level
18. Transient Attributes Attributes in the local object but not in the store Typically used for convenience Example: fullName = “firstName lastName” Requires adding code to generated objects Jedi Level
19. Delete Rules Deny: Don’t allow if some relation exists Nullify: Set relationship to nil Cascade: Delete related objects No Action: Do nothing, I want to cleanup Jedi Level
20. Versioning and Migration MOM is your contract with Core Data If you change your model you must migrate the data to match the new data model Use a custom mapping model for changes Lightweight migration automatically makes minor changes (Snow Leopard/iOS 3.0+) Jedi Level
21. Configurations A persistent store coordinator may only have one MOM One MOM may have many configurations A configuration is a subset of entities Typically used to store different entities in different stores using one store coordinator Jedi Level
22. Demo
23. Resources Apple Documentation Core Data: Apple’s API for Persisting Data on Mac OS X by Marcus S. Zarra https://developer.apple.com/videos/wwdc/2010/
24. Questions?