Core Data系列文章:
[iOS]Core Data浅析一 -- 启用Core Data
[iOS]Core Data浅析二 -- 转换实体(Entity)为模型对象
[iOS]Core Data浅析三 -- 数据的增删改查
以及一个, 在新版Xcode中使用的注意事项:
[Core Data]Xcode 8+ 新建NSManageObject subclass方法
Core Data是iOS中十分重要的一种数据持久化的方式,之前存储数据一直使用的FMDB,很少使用Core Data;但是,还是有必要来了解一下这个高大上的数据持久化的方式的.
由于笔者对此认知有限,不正确的地方还请指正,感谢!
开始之前,我们先来了解一下这几个对象:
NSManagedObjectModel
这个是应用程序的数据模型,这个模型包含实体(Entity),属性(Property),读取请求(Fetch Request)等
NSManagedObjectContext
参与对数据对象进行各种操作的全过程,并检测数据对象的变化,以提供对undo/redo的支持及更新绑定到数据的UI
NSManagedObject
数据记录
NSEntityDescription
数据实体对象
NSPersistentStoreCoordinator
主要处理底层对数据的读取与写入操作,一般我们不需要与他接触;
另外:.xcdatamodeld文件编译后为.momd或者.mom文件
一. 新建工程,并启用Core Data
想要使用Core Data,需要在新建工程的时候勾选(当然也可以手动创建),即在输入工程名称的界面勾选Use Core Data ,如下图:
这样新建的工程,Xcode会帮我们添加一些与Core Data相关的内容,你会发现,在项目的左边列表,多了一个以xcdatamodeld为后缀名的文件,这就是我们的Data Model文件:
这个是默认生成的,当然我们也可以手动添加,和新建其他文件一样:右键-->New File...选择左侧Core Data --> Data Model
Next,输入名称,Create 即可!
和未勾选Core Data的工程的区别还有,就是在AppDelegate中,其中.h文件中多了以下内容:
#import <UIKit/UIKit.h>
#import <CoreData/CoreData.h>
@interface AppDelegate : UIResponder <UIApplicationDelegate>
@property (strong, nonatomic) UIWindow *window;
@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;
@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;
@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
- (void)saveContext;
- (NSURL *)applicationDocumentsDirectory;
@end
在.m文件中,增加了相关的方法的实现,一般在文件的最下面可以看到!
- (void)applicationWillTerminate:(UIApplication *)application {
// Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.
// Saves changes in the application's managed object context before the application terminates.
[self saveContext];
}
#pragma mark - Core Data stack
@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;
- (NSURL *)applicationDocumentsDirectory {
// The directory the application uses to store the Core Data store file. This code uses a directory named "com.artup.LZCoreData" in the application's documents directory.
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}
- (NSManagedObjectModel *)managedObjectModel {
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
if (_managedObjectModel != nil) {
return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"LZCoreData" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}
- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
// The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it.
if (_persistentStoreCoordinator != nil) {
return _persistentStoreCoordinator;
}
// Create the coordinator and store
_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"LZCoreData.sqlite"];
NSError *error = nil;
NSString *failureReason = @"There was an error creating or loading the application's saved data.";
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
// Report any error we got.
NSMutableDictionary *dict = [NSMutableDictionary dictionary];
dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
dict[NSLocalizedFailureReasonErrorKey] = failureReason;
dict[NSUnderlyingErrorKey] = error;
error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
// Replace this with code to handle the error appropriately.
// abort() 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.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
return _persistentStoreCoordinator;
}
- (NSManagedObjectContext *)managedObjectContext {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (!coordinator) {
return nil;
}
_managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
return _managedObjectContext;
}
#pragma mark - Core Data Saving support
- (void)saveContext {
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
NSError *error = nil;
if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error]) {
// Replace this implementation with code to handle the error appropriately.
// abort() 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.
NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
abort();
}
}
}
二 . 添加数据模型的可视化操作
选择LZCoreData.xcdatamodeld文件,所有的可视化操作都是在这个文件进行的;
1.添加一个实体(Entity)
点击下方的+按钮(Add Entity),输入你要建立的实体名称,这里是PeopleEntity
2. 添加一个属性
属性主要显示在中间的Attributes一栏,点击其左下的+,可以新加一个属性,输入名称,并选择一个类型,这里定义一个String类型的name属性:
注意:这里的属性名称首字母必须小写,否则会有如下提示:
这里的数据类型中,有一个比较特殊:Transformble,对应于OC中的id类型;
同样方式,再添加age和sex属性;
然后,再添加一个实体ManEntity,属性设置如下:
3. 建立联系
这里已建立PeopleEntity和ManEntity之间的联系为例,
选择PeopleEntity实体,在中间的Relationships一栏,点击+,添加一个联系,起一个名称,并在Destination中选择ManEntity:
这里的作用相当于,在实体PeopleEntity中添加了一个类型为ManEntity,名称为manRelationship的属性;
Apple官方建议我们在建立一个目标关系后,要建立一个返回关系;即在ManEntity中建立一个和PeopleEntity的联系;
选中一个联系后,在右侧可以设置联系的一些属性:
例如Delete Rule(删除规则),Type(联系类型,一对多,一对一)等;
这样,我们的数据模型就建立好了,接下来的事情,就是如何去使用了.
三. 使用数据模型
接下来的操作主要就是写代码了,来到我们的ViewController.m文件,导入AppDelegate.h头文件,我们需要用到里面关于Core Data的一些内容;新建一个方法test1,添加以下代码:
//获取代理
AppDelegate *delegate = [[UIApplication sharedApplication] delegate];
//获取context
NSManagedObjectContext *context = [delegate managedObjectContext];
//获取PeopleEntity实体
NSManagedObject *people = [NSEntityDescription insertNewObjectForEntityForName:@"PeopleEntity" inManagedObjectContext:context];
//设置属性内容
[people setValue:@"流火绯瞳" forKey:@"name"];
[people setValue:@26 forKey:@"age"];
[people setValue:@0 forKey:@"sex"];
//获取ManEntit实体
NSManagedObject *man = [NSEntityDescription insertNewObjectForEntityForName:@"ManEntity" inManagedObjectContext:context];
[man setValue:@178.0 forKey:@"height"];
[man setValue:@60.0 forKey:@"weight"];
[man setValue:@"张三" forKey:@"name"];
[man setValue:people forKey:@"peopleRelationship"];
[people setValue:man forKey:@"manRelationship"];
NSError *error;
//保存更改
if ([context save:&error]) {
NSLog(@"保存成功");
} else {
NSLog(@"Whoops, couldn't save: %@", [error localizedDescription]);
}
//查询实体
//创建一个查询请求
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
//获取要查询的实体
NSEntityDescription *entity = [NSEntityDescription
entityForName:@"PeopleEntity" inManagedObjectContext:context];
//添加到查询请求
[fetchRequest setEntity:entity];
//开始查询并获取结果
NSArray *fetchedObjects = [context executeFetchRequest:fetchRequest error:&error];
NSLog(@"输出查询结果");
for (NSManagedObject *info in fetchedObjects) {
NSLog(@"Name: %@", [info valueForKey:@"name"]);
NSLog(@"age: %@", [info valueForKey:@"age"]);
NSLog(@"sex: %@", [info valueForKey:@"sex"]);
NSLog(@"-----------------------------------");
NSManagedObject *man1 = [info valueForKey:@"manRelationship"];
NSLog(@"Name: %@", [man1 valueForKey:@"name"]);
NSLog(@"weight: %@", [man1 valueForKey:@"weight"]);
NSLog(@"height: %@", [man1 valueForKey:@"height"]);
NSLog(@"==========================================");
}
代码中我简单的加入了注释,这里只是为了测试一下创建的数据模型是否可用;
所以,只是使用了添加数据和查询数据的方法,然后运行程序,可以在控制台看到如下输出:
2016-05-26 15:37:25.496 LZCoreData[5654:567413] 保存成功
2016-05-26 15:37:25.497 LZCoreData[5654:567413] 输出查询结果
2016-05-26 15:37:25.498 LZCoreData[5654:567413] Name: 流火绯瞳
2016-05-26 15:37:25.498 LZCoreData[5654:567413] age: 26
2016-05-26 15:37:25.498 LZCoreData[5654:567413] sex: 0
2016-05-26 15:37:25.498 LZCoreData[5654:567413] -----------------------------------
2016-05-26 15:37:25.498 LZCoreData[5654:567413] Name: 张三
2016-05-26 15:37:25.499 LZCoreData[5654:567413] weight: 60
2016-05-26 15:37:25.499 LZCoreData[5654:567413] height: 178
2016-05-26 15:37:25.501 LZCoreData[5654:567413] ==========================================
表示我们成功的保存了数据,并查询了出来.
你可能会发现,这里我在设置属性值和取值的时候,都是使用的KVC的模式,这样在使用时是相当不方便的,能不能像其他的Model那样,利用.的形式来赋值取值呢?答案是肯定的.
怎么将我们创建的可视化模型转化为OC的对象模型呢?请移步[iOS]Core Data浅析(二)
