注意: 以下方法适用于iOS10+ swift版本

启用

新建工程时勾选use core data
对于已创建工程，可以新建一个带有core data的工程，拷贝appDelegate中coredata相关代码。然后更改项目名，加入import coreData即可

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.
     */
    //创建持久化容器
    let container = NSPersistentContainer(name: "StructDemo")
    //载入
    container.loadPersistentStores(completionHandler: { (storeDescription, error) in
        //失败时报错
        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 () {
    //获取容器上下文
    let context = persistentContainer.viewContext
    //改变时保存
    if context.hasChanges {
        do {
            //保存
            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.
            //失败时错误处理
            let nserror = error as NSError
            fatalError("Unresolved error \(nserror), \(nserror.userInfo)")
        }
    }
}

可视化建模

• 注意图片类型为binary data
• 注意设置类型optional
• 注意把实体(Entity)的class name改成原名字后面加MO(AreaMO)，代码中Area替换成AreaMO

手动生成类文件

使用可视化建模会自动生成相应文件，但是会隐藏不会显示。
可以通过设置实体属性来阻止自动生成。

image.png

image.png

Relationship

双向关系，一对多。可根据实际情况修改

image.png

image.png

新增

let appDelegate = UIApplication.shared.delegate as! AppDelegate

area = AreaMO(context: appDelegate.persistentContainer.viewContext)
area.name = nameTextField.text
area.province = provinceTextField.text
area.part = partTextField.text
area.isVisited = self.isVisited
if let imageData = coverImageView.image?.jpegData(compressionQuality: 0.7) {
    area.image = imageData
}
print("正在保存")
appDelegate.saveContext()
performSegue(withIdentifier: "unwindToHomeList", sender: self)

查找全部

func fetchAllData() {
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    do {
        //取回后保存在数组中
        areas = try appDelegate.persistentContainer.viewContext.fetch(AreaMO.fetchRequest())
    } catch  {
        print(error)
    }
}

每次更新修改单条数据，都查找全部数据，会造成性能上的浪费，使用一下方法，进行性能优化

NSFetchedResultsController关联

定义变量
var fetchedController: NSFetchedResultsController<AreaMO>!
实现如下方法，并在viewDidLoad中调用

func fetchedControllerFetchData(){
    //初始化请求并设定请求结果类型为AreaMO
    let request: NSFetchRequest<AreaMO>  = AreaMO.fetchRequest()
    //排序方式
    let sortDesc = NSSortDescriptor(key: "name", ascending: true)
    request.sortDescriptors = [sortDesc]
    
    //获取上下文
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext
    
    //根据请求和上下文初始化查询结果控制器
    fetchedController = NSFetchedResultsController(fetchRequest: request, managedObjectContext: context, sectionNameKeyPath: nil, cacheName: nil)
    fetchedController.delegate = self
    
    //执行查询，失败打印错误，成功将结果保存在数组中
    do {
        try fetchedController.performFetch()
        if let objects = fetchedController.fetchedObjects {
            areas = objects
        }
    } catch  {
        print(error)
    }
}

遵循代理NSFetchedResultsControllerDelegate
实现如下代理方法：

func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    //将要变更
    tableView.beginUpdates()
}

func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    //已经变更
    tableView.endUpdates()
}

func controller(_ controller: NSFetchedResultsController<NSFetchRequestResult>, didChange anObject: Any, at indexPath: IndexPath?, for type: NSFetchedResultsChangeType, newIndexPath: IndexPath?) {
    //正在变化
    //根据类型筛选
    switch type {
        //删除指定行
    case .delete:
        tableView.deleteRows(at: [indexPath!], with: .automatic)
        //插入指定行
    case .insert:
        tableView.insertRows(at: [newIndexPath!], with: .automatic)
        //更新指定行
    case .update:
        tableView.reloadRows(at: [indexPath!], with: .automatic)
        //默认全部更新
    default:
        tableView.reloadData()
    }
    
    //同时更新内存数据
    if let objects = controller.fetchedObjects {
        areas = objects as! [AreaMO]
    }
}

删除

因为NSFetchedResultsController的代理方法中，有根据数据变化对单元格进行删除的操作，所以这里不再需要原来的删除操作。避免多次进行单元格删除操作造成崩溃。

let rowActionDelete = UITableViewRowAction(style: .destructive, title: "删除") { (_, _) in
//            self.areas.remove(at: indexPath.row)
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    let context = appDelegate.persistentContainer.viewContext
    context.delete(self.fetchedController.object(at: indexPath))
    appDelegate.saveContext()
//            tableView.deleteRows(at: [indexPath], with: .automatic)
}

更新

在数据更新页面更新数据退出的时候，也就是在如下更新页面退场的方法中，执行一次保存操作。

@IBAction func closeReview(segue:UIStoryboardSegue) {
    let reviewVC = segue.source as! ReviewViewController

    if let rating = reviewVC.rating {
        area.rating = rating
        ratingButton.setImage(UIImage(named: rating), for: .normal)
    }
    let appDelegate = UIApplication.shared.delegate as! AppDelegate
    appDelegate.saveContext()
}

注意：以下为早期OC版本代码

1.查找全部

 - （NSMutableArray） findAll
{
    获取上下文
    NSManagedObjectContext *cxt = [self managedObjectContext];
    根据上下文建立实体描述
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName@"Note" inManagedObjecctContext:cxt];
    根据实体描述建立请求
    NSFetchRequset *request = [[NSFetchRequset alloc] init];
    [request setSortDescriptors:@[sortDescriptor]];
    
    建立用于装错误信息的error地址    
    NSError *error = nil;
    在上下文中根据请求从数据库中取得装有NoteManagedObject对象的数组
    NSArray *listData = [cxt executeFestchRequest:request error:&error];
    
    建立准备装有目标模型的数组
    NSMutableArray *resListData = [[NSMutableArray alloc] init];
    
    重装
    for(BoteManagedObject *mo in listData){
        Note *note = [[Note alloc] init];
        note.date = mo.date;
        mote.content = mo.content;
        [resListDate addObject:note];
    }

    return resListData;
}

2.条件查找

- （NSMutableArray） findById:(Note *)model
{
    获取上下文
    NSManagedObjectContext *cxt = [self managedObjectContext];
    根据上下文建立实体描述
    NSEntityDescription *entityDescription = [NSEntityDescription entityForName@"Note" inManagedObjecctContext:cxt];
    根据实体描述建立请求
    NSFetchRequset *request = [[NSFetchRequset alloc] init];
    [request setSortDescriptors:@[sortDescriptor]];

    添加具体的查找条件
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"date = %@" , model.date];
    [request setPredicate : predicate];
    
    建立用于装错误信息的error地址    
    NSError *error = nil;
    在上下文中根据请求从数据库中取得装有NoteManagedObject对象的数组
    NSArray *listData = [cxt executeFestchRequest:request error:&error];
    
    建立准备装有目标模型的数组
    NSMutableArray *resListData = [[NSMutableArray alloc] init];
    
    重装
    for(BoteManagedObject *mo in listData){
        Note *note = [[Note alloc] init];
        note.date = mo.date;
        mote.content = mo.content;
        [resListDate addObject:note];
    }

    return resListData;
}

3.增加数据

- （int）creat：（Note*）model
{
    NSManagedObjectContext *cxt = [self managedObjectContext];
    
    建立新的
    NoteManagedObject *note = [NSEntityDescription insertNewObjectForEntityForName:@"Note" inManagedObjectContext:cxt];
    [note setValue: model.content forKey:@"content"];
    [note setValue: model.date forKey:@"date"];

    note.date = model.date;
    note.content = model.content; 

    NSError *savingError = nil;
    if([self.managedObjectContext save:&savingError]){
            NSLog(@"插入数据成功");
     } else {
            NSLog(@"插入数据失败");
            return -1;
     }
    retrun 0;
 }

4.删除数据

- （int） remove:(Note*)model
{
    NSManagedObjectContext *cxt = [self managedObjectContext];

    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Note"  inManagedObjectCOntext:cxt];

    NSFetchRequest *request = [[NSFetchRequest alloc] init]；
    [request setEntity:entityDescription];
    
    NSPredicate *predicate = [NSPredicate prediccateWithFormat:@"date  = %@" , model.date]；
    [request setPredicate:predicate]；
    
    NSError *error = nil；
    NSArray *listData = [cxt executeFetchRequest:request error:&error];
    if([listData count] > 0){
           NoteManagedObject *note = [listData lastObject]；
           [self.managedObjectContext deleteObject:note]；
           
           NSError *savingError = nil;
           if([self.managedObjectContext save:&savingError]){
                NSLog(@"删除数据成功");
            } else{
                NSLog(@"删除数据失败");
                return -1;
            }
    } 
    return 0;
}

5.修改数据

-（int）modify:(Note*)model
{
    NSManagedObjectContext *cxt = [self managedObjectContext];

    NSEntityDescription *entityDescription = [NSEntityDescription entityForName:@"Note" inManagedObjectContext:cxt]；

    NSFetchRequest *request = [[NSFetchRequset alloc] init];
    [requset setEntity:entityDescription]；

    NSError *error = nil;
    NSArray *listData = [cxt executeFetchRequest:request error:&error];
    if([listData count] > 0){
        NoteManagedObject *note = [listData lastObject]；
        note.content = model.content;

        NSError *savingError = nil;
        if([self.managedObjectContext save:&savingError]){
            NSLog(@"修改数据成功");
        }else{
            NSLog(@"修改数据失败");
            return -1;
        }
    }
    return 0;
}