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: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] 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 = @20;
    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] + 2);
            
            
            //删除对象
            if(idx == 2)
            {
                [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;
}