iOS:CoreData数据库的使用一(创建单个数据库表)

CoreData数据库框架：mac系统自带的数据库，它是苹果公司对sqlite进行封装而来的，既提供了对数据库的主要操作，也提供了具体的视图关系模型。

需要用到三个对象：

1•Managed Object Model（被管理对象模型）: 

        数据库的轮廓，或者结构。包含了各个实体的定义信息

2•Persistent Store Coordinator （持久性数据协调器）：

        数据库连接库，在这里设置数据存储的名字和位置，以及数据存储的时机

3•Managed Object Context （被管理对象上下文）：

                数据的实际内容，基本上，插入数据，查询数据，删除数据的工作都在这里完成

 

三者关系图显示：

        

 

 

 

•Persistent store     //持久化存储

•Persistent store coordinator    //持久化存储协调器

•Managed object model (MOM)    //被管理对象的数据模型(对实例对象进行描述)

•Managed object    //被管理对象

•Managed object context (MOC) //被管理的实例对象

 

使用步骤如下：

1、创建项目时,勾选CoreData选项。

2、此时项目文件中多了一个CoreData___.xcdatamodel文件，选中该文件，进入其创建数据库表格界面，在界面的左下角点击Add Entity添加实体对象，并设置该对象的类名；与此同时，在AppDeletegate类中，自动声明和定义了需要的三个对象Managed Object Model，Persistent Store Coordinator，Managed Object Context ，并且自动封装了大量的sqlite的函数方法。

3、在attributes选项处添加该实体对象的属性。

4、选中该实体类，在模拟器选项上点击Editor下的create Managed Object Context subclass..创建Managed Object Context的子类。

5、这个子类中，编译器自动生成了所添加的所有属性。

6、在应用程序代理类中用代码对数据库进行操作。

 

创建实体对象(设置类名为Person)截图如下：　　　　　　添加其属性截图如下：

 

所有产生的文件截图如下：　　　　　　　　　　 创建的数据库表视图如下：

              

 

具体代码如下：

AppDelegate.h（自动生成的代码）

 #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

AppDelegate.m(自动生成的代码，封装的是sqlite的一些函数方法)

 #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.bjsxt.CoreData___" 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:@"CoreData___" withExtension:@"momd"];
     _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
     return _managedObjectModel;
 }

 - (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
     // The persistent store coordinator for the application. This implementation creates and return 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:@"CoreData___.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: 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] init];
     [_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();
         }
     }
 }

Person.h(自动生成的代码)

 #import <Foundation/Foundation.h>
 #import <CoreData/CoreData.h>

 @interface Person : NSManagedObject

 @property (nonatomic, retain) NSString * name;
 @property (nonatomic, retain) NSNumber * age;
 @property (nonatomic, retain) NSNumber * gender;

 @end

Person.m(自动生成的代码)

 #import "Person.h"

 @implementation Person

 @dynamic name;
 @dynamic age;
 @dynamic gender;

 @end

重点来了，对数据库进行的主要操作，需要人为代码写的：

在AppDelegate.m文件中进行：

 - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {

     //创建实体对象
     Person *person = [NSEntityDescription insertNewObjectForEntityForName:NSStringFromClass([Person class]) inManagedObjectContext:self.managedObjectContext];

     //设置实体对象的属性
     person.name = @"zhangsan";
     person.age = @;
     person.gender = @'M';

     //保存数据
     [self saveContext];

     //查询实体对象的数据
     //1.创建请求对象
     NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:NSStringFromClass([person class])];
     //2.创建排序对象
     NSSortDescriptor *ageSort = [NSSortDescriptor sortDescriptorWithKey:@"age" ascending:YES];
     //3.发出请求
     [request setSortDescriptors:@[ageSort]];
     //4.执行查询
     NSError *error = nil;
     NSArray *persons = [self.managedObjectContext executeFetchRequest:request error:&error];
     if(!error)
     {
         //遍历所有的实体对象
         [persons enumerateObjectsUsingBlock:^(Person *person, NSUInteger idx, BOOL *stop) {
             NSLog(@"name:%@,age:%@,gender:%c",person.name,person.age,(char)[person.gender integerValue]);

             //修改对象
             person.age = @([person.age integerValue] + );

             //删除对象
             if(idx == )
             {
                 [self.managedObjectContext deleteObject:person];
                 NSError *error = nil;
                 [self.managedObjectContext save:&error];
                 if([person isDeleted])
                 {
                     NSLog(@"删除成功");
                 }
             }
         }];
     }

     //保存上下文
     [self saveContext];

     return YES;
 }