Using Core Data in Swift

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USING CORE DATA IN SWIFT JESSE SQUIRES JESSESQUIRES.COM • @JESSE_SQUIRES • GITHUB/JESSESQUIRES

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WHAT IS CORE DATA?

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The Core Data framework provides generalized and automated solutions to common tasks associated with object life-cycle and object graph management, including persistence. — Core Data Programming Guide

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Core Data is backed by a SQLite database. However, it is not a relational database or RDBMS.

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BACKED BY SQLITE. NOT A DATABASE?

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CORE DATA MANAGES: LIFE-CYCLE GRAPH PERSISTENCE SEARCHING OF OBJECTS

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CORE DATA STACK: Managed objects NSMangedObject Managed object context NSManagedObjectContext Persistent Store Coordinator NSPersistentStoreCoordinator Persistent Store NSPersistentStore SQLite

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WHY USE CORE DATA? ▸ Provides featues you need ▸ "Mature, unit tested, optimized" ▸ Part of iOS and OS X toolchain ▸ Apple continues to invest heavily in it ▸ Popular, tons of resources online

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WHY USE SWIFT? ▸ Clarity ▸ Type-safety ▸ Swift-only features ▸ Functional paradigms

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SWIFT + CORE DATA

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WARNING: TOOLS ARE IMMATURE SourceKitService Terminated Editor functionality temporarily limited.

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STANDING UP THE CORE DATA STACK Same boilerplate code as Objective-C Better in Swift

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CORE DATA STACK struct CoreDataModel { let name: String let bundle: NSBundle init(name: String, bundle: NSBundle) // other properties & methods }

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CORE DATA STACK class CoreDataStack { let model: CoreDataModel let managedObjectContext: NSManagedObjectContext let persistentStoreCoordinator: NSPersistentStoreCoordinator init(model: CoreDataModel, storeType: String, concurrencyType: NSManagedObjectContextConcurrencyType) // other properties and methods }

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CORE DATA STACK let model = CoreDataModel(name: "MyModel", bundle: myBundle) let stack = CoreDataStack(model: model, storeType: NSSQLiteStoreType, concurrencyType: .MainQueueConcurrencyType) // Use context stack.managedObjectContext

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CORE DATA STACK AppDelegate.m DO NOT

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USE FRAMEWORKS Clear model namespace, Modular, Reusable, Unit Testing

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CREATING MANAGED OBJECTS ▸ Xcode generated classes are terrible ▸ mogenerator Swift support still experimental (Last release Sept 2014)

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CREATING MANAGED OBJECTS VISUAL MODEL EDITOR

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CREATING MANAGED OBJECTS ATTRIBUTE VALIDATION

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OBJECTIVE-C @interface Employee : NSManagedObject @property (nonatomic, retain) NSString * address; @property (nonatomic, retain) NSDate * dateOfBirth; @property (nonatomic, retain) NSString * email; @property (nonatomic, retain) NSString * name; @property (nonatomic, retain) NSDecimalNumber * salary; @property (nonatomic, retain) NSNumber * status; @end

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SWIFT class Employee: NSManagedObject { @NSManaged var address: String? @NSManaged var dateOfBirth: NSDate @NSManaged var email: String? @NSManaged var name: String @NSManaged var salary: NSDecimalNumber @NSManaged var status: Int32 }

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OPTIONALS Xcode will generate String instead of String? @property (nonatomic, retain) NSString * address; @NSManaged var address: String?

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CREATING MANAGED OBJECTS PREFIXED SUBCLASSES NSManagedObject . Swift namespaces

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Xcode does not prefix classes automatically Must add prefix manually after generating classes No prefix means runtime crash, obscure errors

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INSTANTIATING MANAGED OBJECTS Reduce boilerplate, generalize NSEntityDescription

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THE OBJECTIVE-C WAY // "Person" NSString *name = [Person entityName]; @implementation NSManagedObject (Helpers) + (NSString *)entityName { return NSStringFromClass([self class]); } @end

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THE OBJECTIVE-C WAY // Create new person Person *person = [Person insertNewObjectInContext:context]; @implementation NSManagedObject (Helpers) + (instancetype)insertNewObjectInContext:(NSManagedObjectContext *)context { return [NSEntityDescription insertNewObjectForEntityForName:[self entityName] inManagedObjectContext:context]; } @end

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THE SWIFT WAY? // "MyApp.Person" let fullName = NSStringFromClass(object_getClass(self)) extension NSManagedObject { class func entityName() -> String { let fullClassName = NSStringFromClass(object_getClass(self)) let nameComponents = split(fullClassName) { $0 == "." } return last(nameComponents)! } } // "Person" let entityName = Person.entityName()

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THE SWIFT WAY? // Create new person let person = Person(context: context) extension NSManagedObject { convenience init(context: NSManagedObjectContext) { let name = self.dynamicType.entityName() let entity = NSEntityDescription.entityForName(name, inManagedObjectContext: context)! self.init(entity: entity, insertIntoManagedObjectContext: context) } }

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THE SWIFT WAY? class Employee: NSManagedObject { init(context: NSManagedObjectContext) { let entity = NSEntityDescription.entityForName("Employee", inManagedObjectContext: context)! super.init(entity: entity, insertIntoManagedObjectContext: context) } }

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NOT VERY SWIFT "OBJECTIVE-C WITH A NEW SYNTAX"

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THE OBJECTIVE-C WAY IS NOT ALWAYS THE SWIFT WAY

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EMBRACE THE SWIFTNESS

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SWIFT DESIGNATED INITIALIZERS

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1. Stored properties must be assigned initial value 2. Designated init fully initializes all properties 3. Convenience init are secondary 4. Convenience init must call designated init 5. Superclass initializers not inherited in subclasses by default

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DESIGNATED INITIALIZERS? // designated init init(entity:insertIntoManagedObjectContext:) // our convenience init convenience init(context:)

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CORE DATA BYPASSES INITIALIZATION RULES @NSManaged

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class Employee: NSManagedObject { init(context: NSManagedObjectContext, name: String, dateOfBirth: NSDate, salary: NSDecimalNumber, employeeId: String = NSUUID().UUIDString, email: String? = nil, address: String? = nil) { // init } }

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typealias

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TYPEALIAS typealias EmployeeId = String class Employee: NSManagedObject { @NSManaged var employeeId: EmployeeId } // Example let id: EmployeeId = "12345"

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RELATIONSHIPS NSSet Set

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Set Nope

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enum

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ENUM enum Genre: String { case BlackMetal = "Black Metal" case DeathMetal = "Death Metal" case DoomMetal = "Doom Metal" case FolkMetal = "Folk Metal" case Grindcore = "Grindcore" case Hardcore = "Hardcore" case CrustPunk = "Crust Punk" case StreetPunk = "Street Punk" case Thrash = "Thrash" }

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ENUM public class Band: NSManagedObject { @NSManaged private var genreValue: String public var genre: Genre { get { return Genre(rawValue: self.genreValue)! } set { self.genreValue = newValue.rawValue } } }

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ENUM // old band.genre = "Black Metal" // new band.genre = .BlackMetal

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ENUM Unfortunately, must use private property for fetch requests let fetch = NSFetchRequest(entityName: "Band") fetch.predicate = NSPredicate(format: "genreValue == %@", genre)

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FUNCTIONAL PARADIGMS WITH MICRO-LIBRARIES

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SAVING var error: NSError? let success: Bool = managedObjectContext.save(&error) // handle success or error

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SAVING func saveContext(context:) -> (success: Bool, error: NSError?) // Example let result = saveContext(context) if !result.success { println("Error: \(result.error)") }

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FETCH REQUESTS var error: NSError? var results = context.executeFetchRequest(request, error: &error) // [AnyObject]? if results == nil { println("Error = \(error)") }

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FETCH REQUESTS // T is a phantom type class FetchRequest : NSFetchRequest { init(entity: NSEntityDescription) { super.init() self.entity = entity } }

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FETCH REQUESTS typealias FetchResult = (success: Bool, objects: [T], error: NSError?) func fetch (request: FetchRequest, context: NSManagedObjectContext) -> FetchResult

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FETCH REQUESTS typealias FetchResult = (success: Bool, objects: [T], error: NSError?) func fetch (request: FetchRequest, context: NSManagedObjectContext) -> FetchResult { var error: NSError? if let results = context.executeFetchRequest(request, error: &error) { return (true, results as! [T], error) } return (false, [], error) }

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FETCH REQUESTS // Example let request = FetchRequest(entity: entityDescription) let results = fetch(request: request, inContext: context) if !results.success { println("Error = \(results.error)") } results.objects // [Band]