CoreData的简单使用-Swift

一、Core Data介绍

1、Core Data是iOS5之后才出现的一个数据持久化存储框架，它提供了对象-关系映射(ORM)的功能，即能够将对象转化成数据，也能够将保存在数据库中的数据还原成对象。
2、虽然其底层也是由类似于SQL的技术来实现，但我们不需要编写任何SQL语句，有点像Java开发中的Hibernate持久化框架
3、Core Data数据最终的存储类型可以是：SQLite数据库，XML，二进制，内存里，或自定义数据类型。
4、与SQLite区别：只能取出整个实体记录，然后分解，之后才能得到实体的某个属性。

二、Core Data的使用准备 - 数据模型和实体类的创建

1、创建项目的时候，勾选“Use Core Data”。完毕后在 AppDelegate 中，会生成相关代码。

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2、打开项目中的 xcdatamodeld 文件，在右边的数据模型编辑器的底部工具栏点击 Add Entity 添加实体。
同时在属性栏中对实体命名进行修改，并在 Attribute 栏目中添加属性。

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3、点击下方的 Editor Style 按钮可以查看实体的关系图。

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4、自 iOS10 和 swift3 之后，访问 CoreData 的方法简洁了许多，我们不再需要手动新建对应于 entity 的 class。

三、Core Data的使用

1、首先在代码中引入CoreData库

import CoreData

2、插入（保存）数据操作

/// 添加数据
func addData()
{
    //获取管理的数据上下文 对象
    let app = UIApplication.shared.delegate as! AppDelegate
    let context = app.persistentContainer.viewContext

    //创建User对象
    let user = NSEntityDescription.insertNewObject(forEntityName: "User",
                                                   into: context) as! User

    //对象赋值
    user.id = 1
    user.userName = "hangge"
    user.password = "1234"

    //保存
    do {
        try context.save()
        print("保存成功！")
    } catch {
        fatalError("不能保存：\(error)")
    }
}

3、删除数据操作

/// 删除数据操作
func deleteData()
{
    //获取管理的数据上下文 对象
    let app = UIApplication.shared.delegate as! AppDelegate
    let context = app.persistentContainer.viewContext

    //声明数据的请求
    let fetchRequest = NSFetchRequest(entityName:"User")
    fetchRequest.fetchLimit = 10 //限定查询结果的数量
    fetchRequest.fetchOffset = 0 //查询的偏移量

    //设置查询条件
    let predicate = NSPredicate(format: "id= '1' ", "")
    fetchRequest.predicate = predicate

    //查询操作
    do {
        let fetchedObjects = try context.fetch(fetchRequest)

        //遍历查询的结果
        for info in fetchedObjects{
            //删除对象
            context.delete(info)
        }

        //重新保存-更新到数据库
        try! context.save()
    }
    catch {
        fatalError("不能保存：\(error)")
    }
}

4、修改数据操作

/// 修改数据操作
func modifyData()
{
    //获取管理的数据上下文 对象
    let app = UIApplication.shared.delegate as! AppDelegate
    let context = app.persistentContainer.viewContext

    //声明数据的请求
    let fetchRequest = NSFetchRequest(entityName:"User")
    fetchRequest.fetchLimit = 10 //限定查询结果的数量
    fetchRequest.fetchOffset = 0 //查询的偏移量

    //设置查询条件
    let predicate = NSPredicate(format: "id= '1' ", "")
    fetchRequest.predicate = predicate

    //查询操作
    do {
        let fetchedObjects = try context.fetch(fetchRequest)

        //遍历查询的结果
        for info in fetchedObjects{
            //修改密码
            info.password = "abcd"
            //重新保存
            try context.save()
        }
    }
    catch {
        fatalError("不能保存：\(error)")
    }
}

5、查询数据操作

/// 查询数据
func queryData()
{
    //获取管理的数据上下文 对象
    let app = UIApplication.shared.delegate as! AppDelegate
    let context = app.persistentContainer.viewContext

    //声明数据的请求
    let fetchRequest = NSFetchRequest(entityName:"User")
    fetchRequest.fetchLimit = 10 //限定查询结果的数量
    fetchRequest.fetchOffset = 0 //查询的偏移量

    //设置查询条件
    let predicate = NSPredicate(format: "id= '1' ", "")
    fetchRequest.predicate = predicate

    //查询操作
    do {
        let fetchedObjects = try context.fetch(fetchRequest)

        //遍历查询的结果
        for info in fetchedObjects{
            print("id=\(info.id)")
            print("username=\(info.userName)")
            print("password=\(info.password)")
        }
    }
    catch {
        fatalError("不能保存：\(error)")
    }
}

若项目并未在创建时勾选coreData手动添加 Cord Data 支持

1、首先在项目中创建一个 xcdatamodeld 文件（Data Model）、文件名建议与项目名一致

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2、然后打开 AppDelegate.swift，在里面添加 Core Data 相关的支持方法（黄色部分）

import UIKit
import CoreData

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {



    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        // Override point for customization after application launch.
        return true
    }

    // MARK: UISceneSession Lifecycle

    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)
    }

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set) {
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    }

    // MARK: - Core Data stack

    lazy var persistentContainer: NSPersistentContainer = {
        /*
         The persistent container for the application. This implementation
         creates and returns a container, having loaded the store for the
         application to it. This property is optional since there are legitimate
         error conditions that could cause the creation of the store to fail.
        */
        let container = NSPersistentContainer(name: "CoreDataDemo")
        container.loadPersistentStores(completionHandler: { (storeDescription, error) in
            if let error = error as NSError? {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                 
                /*
                 Typical reasons for an error here include:
                 * The parent directory does not exist, cannot be created, or disallows writing.
                 * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                 * The device is out of space.
                 * The store could not be migrated to the current model version.
                 Check the error message to determine what the actual problem was.
                 */
                fatalError("Unresolved error \(error), \(error.userInfo)")
            }
        })
        return container
    }()

    // MARK: - Core Data Saving support

    func saveContext () {
        let context = persistentContainer.viewContext
        if context.hasChanges {
            do {
                try context.save()
            } catch {
                // Replace this implementation with code to handle the error appropriately.
                // fatalError() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
                let nserror = error as NSError
                fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
            }
        }
    }

}

参考：

https://www.hangge.com/blog/cache/detail_767.html
https://www.hangge.com/blog/cache/detail_1841.html#