Using Core Data in Swift

Core Data is probably loved as much as it is shunned by iOS developers. No matter its pros and cons, it remains a popular choice for many iOS developers as Apple continues to invest in it. Core Data is a framework of great power that often comes with great frustration. When using Swift, we can make Core Data more powerful, and sometimes more frustrating. This talk presents practical strategies for moving away from an Objective-C model, the bugs you'll run into and how to work around them, how Swift can bring clarity to your model objects, and how to harness Swift features in your NSManagedObject subclasses.

Video:
https://realm.io/news/jesse-squires-core-data-swift/

GitHub project:
https://github.com/jessesquires/JSQCoreDataKit

Event:
https://www.meetup.com/swift-language/events/220612410/

Transcript

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

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2. WHAT IS CORE DATA?
   

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

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5. BACKED BY SQLITE.
   NOT A DATABASE?
   

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

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

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

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10. SWIFT + CORE DATA
    

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

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

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

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14. 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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15. 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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16. CORE DATA STACK
    AppDelegate.m
    DO NOT
    

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

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

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19. CREATING MANAGED OBJECTS
    VISUAL MODEL EDITOR
    

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20. CREATING MANAGED OBJECTS
    ATTRIBUTE VALIDATION
    

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21. 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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22. 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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23. OPTIONALS
    Xcode will generate String instead of String?
    @property (nonatomic, retain) NSString * address;
    @NSManaged var address: String?
    

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24. CREATING MANAGED OBJECTS
    PREFIXED SUBCLASSES
    NSManagedObject
    .
    Swift namespaces
    

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

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26. INSTANTIATING
    MANAGED OBJECTS
    Reduce boilerplate, generalize
    NSEntityDescription
    

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

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28. 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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29. 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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30. 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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31. 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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32. NOT VERY SWIFT
    "OBJECTIVE-C WITH A NEW SYNTAX"
    

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33. THE OBJECTIVE-C WAY
    IS NOT ALWAYS
    THE SWIFT WAY
    

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34. EMBRACE
    THE SWIFTNESS
    

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35. SWIFT DESIGNATED
    INITIALIZERS
    

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

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38. CORE DATA BYPASSES
    INITIALIZATION RULES
    @NSManaged
    

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39. 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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40. typealias
    

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

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42. RELATIONSHIPS
    NSSet
    Set
    

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43. Set
    Nope
    

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44. enum
    

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45. 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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46. 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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47. ENUM
    // old
    band.genre = "Black Metal"
    // new
    band.genre = .BlackMetal
    

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

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49. FUNCTIONAL
    PARADIGMS
    WITH MICRO-LIBRARIES
    

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

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

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

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

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

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55. 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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56. 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]
    

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57. SLIGHTLY LESS TERRIBLE?
    

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58. CLARITY
    OPTIONALS, ENUMS, TYPEALIAS, DESIGNATED INIT
    

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59. SAFETY
    TYPES, GENERICS, DESIGNATED INIT
    

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60. SWIFTNESS
    ENUMS, TYPEALIAS, OPTIONALS
    

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61. FUNCTIONAL
    SAVING, FETCHING, MORE
    

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62. github.com/jessesquires/JSQCoreDataKit
    

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63. Thank you!
    

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64. QUESTIONS?
    JESSESQUIRES.COM • @JESSE_SQUIRES • GITHUB/JESSESQUIRES
    

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