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。
CoreData项目创建.png
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。
3、点击下方的 Editor Style 按钮可以查看实体的关系图。
创建coreData代码.png
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、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<User>(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)")
}
}
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<User>(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、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<User>(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)")
}
}
附：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）。
image.png
（2）文件名建议与项目名一致
（3）接着打开 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<UISceneSession>) {
// 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)")
}
}
}
}
（4）经过上面的配置后，现在的项目就可以使用 CoreData 了
参考：
https://www.hangge.com/blog/cache/detail_767.html
https://www.hangge.com/blog/cache/detail_1841.html#
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