CoreData初次實踐(一)

今天咱們來經過建立一個小的Demo來實踐咱們的CoreDate 的學習。參考書籍Core_Data_by_Tutorials

初始項目

更多關於CoreDate的基礎知識

二

建立Core Data Stack

主要一下幾個步驟：

1. NSManagedObjectModel

2. NSPresistentStore

3. NSPersistentStoreCoordinator

4. NSManagedObjectContext
   在這裏就很少說每個都是什麼了，能夠參考上邊給出的兩篇博客

Show your code

import CoreData

class CoreDadaStack {
   /// model Name
   private let modelName = "Dog Walk"
   /// Document Directory URL
   private lazy var applicationDocumentsDirectory: NSURL = {
       let urls = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)
       return urls[urls.count - 1]
   }()
   
   /// Managed Object Model
   private lazy var managedObjectModel: NSManagedObjectModel = {
       let modelURL = NSBundle.mainBundle().URLForResource(self.modelName, withExtension: "momd")
       return NSManagedObjectModel(contentsOfURL: modelURL!)!
   }()
   /// Presistent Store Coordinator
   private lazy var psc: NSPersistentStoreCoordinator = {
       let coordinator = NSPersistentStoreCoordinator(managedObjectModel: self.managedObjectModel)
       let url = self.applicationDocumentsDirectory.URLByAppendingPathComponent(self.modelName)
       do {
           let options = [NSMigratePersistentStoresAutomaticallyOption:true]
           try coordinator.addPersistentStoreWithType(NSSQLiteStoreType, configuration: nil, URL: url, options: options)
       }catch {
           print("添加持久化存儲區錯誤")
       }
       return coordinator
   }()
   /// Managed Object Context
   lazy var context: NSManagedObjectContext = {
       var managedObjectContext = NSManagedObjectContext(concurrencyType: .MainQueueConcurrencyType)
       managedObjectContext.persistentStoreCoordinator = self.psc
       return managedObjectContext
   }()
   /**
    Save Context Data
    */
   func saveContext() {
       if context.hasChanges {
           do {
               try context.save()
           } catch let error as NSError {
               print("錯誤 ❌ \(error.localizedDescription)")
               abort()
           }
       }
   }
}

選擇ViewController.swift添加下邊代碼
import CoreData

添加屬性：
var managedContext: NSManagedObjectContext!

而後打開AppDelegate.swift

import CoreData
添加屬性：

lazy var coreDataStack = CoreDataStack()

在application(_:didFinishLaunchingWithOptions:)添加下邊代碼

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
    
    let navigationController = window?.rootViewController as! UINavigationController
    let viewcontroller = navigationController.topViewController as! ViewController
    viewcontroller.managedContext = coreDataStack.context
    return true
  }

最後咱們在 UIApplicationDelegate的兩個方法中調用存儲方法

func applicationWillTerminate(application: UIApplication) {
        coreDataStack.saveContext()
    }
    
func applicationDidEnterBackground(application: UIApplication) {
        coreDataStack.saveContext()
    }

Modeling your data

打開Dog Walk

添加 Dog Entity ,添加屬性 name 類型爲 String

添加 Walk Entity, 添加屬性 date 類型爲 Date

接下來咱們完成關係。

打開 Dog Entity ,添加relationship name 爲 walks Set the destination to Walk
在屬性版中修改Type類型，To Many ,勾選 Ordered

打開 Walk Entity , 添加relationship name 爲 dog relationship 爲 Dog Set the destination as dog and the inverse as walks.

Adding managed object subclasses

command + n 選擇 NSManagedObject Subclass 選擇 Dog Walk model 而且選中 Dog 和 Walk entities。 語言選擇 Swift

我在生成的Walk.swift和 Dog.swift中都重寫了父類的方法，爲了在生成這兩個類的時候有代碼提示。

override init(entity: NSEntityDescription, insertIntoManagedObjectContext context: NSManagedObjectContext?) {
        super.init(entity: entity, insertIntoManagedObjectContext: context)
    }

A walk down persistence lane

若是你上邊的步驟都已經完成了，那麼咱們就能夠開始存儲數據了。

首先在ViewController.swift中添加一個屬性 var currentDog: Dog! 而後咱們在viewDidLoad()中來添加一些數據

//建立一個 Entity
let dogEntity = NSEntityDescription.entityForName("Dog", inManagedObjectContext: managedContext)
   let dogName = "Fido"
   //首先來檢查在數據庫中是否存在一個名爲 Fido  的狗過
       let dogFetch = NSFetchRequest(entityName: "Dog")
   dogFetch.predicate = NSPredicate(format: "name == %@", dogName)
   do{
   //執行查詢
       let results = try managedContext.executeFetchRequest(dogFetch) as! [Dog]
       //若是這個狗狗存在的話直接獲取賦值給 currentDog
       if results.count > 0 {
           currentDog = results.first
       }else {
       //若是不存在 則實例化一個Dog
           currentDog = Dog(entity: dogEntity!, insertIntoManagedObjectContext: managedContext)
           currentDog.name = dogName
           try managedContext.save()
       }
   }catch let error as NSError{
       print("Error:\(error)" + "description:\(error.localizedDescription)")
   }

接下來咱們來實現點擊添加按鈕以後添加新狗狗散步時間的功能。

@IBAction func add(sender: AnyObject) {
   //添加一個新的 Walk Entity into Core Data
    let walkEntity = NSEntityDescription.entityForName("Walk", inManagedObjectContext: managedContext)
   let walk = Walk(entity: walkEntity!, insertIntoManagedObjectContext: managedContext)
   walk.date = NSDate.timeIntervalSinceReferenceDate()
   
   //insert the new walk into the dog's walks set
   let walks = currentDog.walks!.mutableCopy() as! NSMutableOrderedSet
   walks.addObject(walk)
   currentDog.walks = walks.copy() as? NSOrderedSet
   //save the managed object context
   do {
       try managedContext.save()
   }catch let error as NSError {
       print("Could not save:\(error)")
   }
   
   tableView.reloadData()
 }

如今你運行程序，點擊➕就能夠看到有新的數據在列表中顯示。

Deleting objects from Core Data

咱們接下來就是要把咱們添加的數據刪除。
咱們來重寫下邊的方法

func tableView(tableView: UITableView, commitEditingStyle editingStyle: UITableViewCellEditingStyle, forRowAtIndexPath indexPath: NSIndexPath) {
        if editingStyle == .Delete {
           //選擇要刪除的walk
           let walkToRemove = currentDog.walks![indexPath.row] as! Walk
           //刪除
           managedContext.deleteObject(walkToRemove)
           do {
               //保存操做
               try managedContext.save()
           }catch let error as NSError {
               print("Could not save: \(error)")
           }
           // 刪除視圖中的數據
           tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Automatic)
       }
 }

運行你的app 來試試吧。

完成的項目