Core Data

• Core Data 是 iOS SDK 里的一个很强大的框架,允许程序员以面向对象的方式储存和管理数据。使用 Core Data 框架,程序员可以很轻松有效地通过面向对象的接口管理数据

•

Core Data
框架提供了
对象
-
关系映射
(ORM)
的功能,即能够将
OC
对象转化成数据,保存在
SQLite3
数据库文件中,也能够将保存在数据库中的数据还原成
OC
对象

•

在数据操作过程中,无需编写任何
SQL
语句

•
要使用
Core Data
,
需要导入
CoreData
框架

Core Data 主要对象

•

NSManagedObjectContext
:负责应用和数据库之间的交互
(CRUD)

•

NSPersistentStoreCoordinator
:添加持久化存储库(如
SQLite
数据库),
是物理数据存储的物理文件和程序之间的联系的桥梁
,负责管理
不同对象上下文

•

NSManagedObjectModel
:被管理的对象模型

三者关系参考：

#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 "nyhx.Core_Data" 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:@"Core_Data" 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:@"Core_Data.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] 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();

        }

    }

}

• NSEntityDescription :实体描述

新增记录（NSEntityDescription）

//_context--->NSManagedObjectContext

Person

*p = [
NSEntityDescription
insertNewObjectForEntityForName
:
@"Person"
inManagedObjectContext
:
_context
];

p.
name

=

@"
张三
"
; p.
age

=

@18
;

[
_context

save
:
nil
];

查询数据（NSFetchRequest）

NSFetchRequest

*request = [
NSFetchRequest
fetchRequestWithEntityName
:
@"Person"
];

request.
predicate

= [
NSPredicate
predicateWithFormat
:
@"%K LIKE '*52*' OR name CONTAINS '
三
'"
,

@"phoneNo"
];

NSArray

*array = [
_context
executeFetchRequest
:request

error
:
nil
];