• CoreData数据持久化框架是Cocoa API的一部分,首次在iOS5版本中出现,它允许按照实体-属性-值模式组织数据,并以XML,二进制文件或者SQLite数据文件的格式持久化数据.
• CoreData主要提供的对象-关系映射(ORM)功能,把OC对象转化为数据保存到文件,也可以数据转化为OC对象

CoreData和SQLite的比较

• SQLite
  1 基于C接口,需要使用sql语句,代码繁琐
  2 在处理大量数据时,表关系更直观
  3 在OC中是不是可视化的
• CoreData
  1 可视化,有undo/redo能力
  2 可以实现多种文件格式 NSSQLiteStoreType,NSBinaryStoreType,NSInMemoryStore Type,NSXMLStoreType.
  3.苹果官方API支持,与iOS结合更紧密

CoreData核心对象

• NSManagedObjectContext 数据管理器器类（负责应用和数据库之间的交互）
• NSManagedObjectModel 数据模型器类（当对于可视化创建model的基类）
• NSPersistentStoreCoordinator 数据协调器类 (添加持久化数据库)
• NSEntityDescription 实体描述类(用来描述实体类)

CoreData数据库框架的核心对象

• NSPersistentStore:持久化存储,一个被封装好的底层类,用于存储数据
• 存储文件:用来存储和管理数据的文件
  1 NSSQLiteStoreType
  2 NSBinaryStoreType
  3 NSInMemoryStoreType
  4 NSXMLStoreType.
• NSManagedObjectContext:被管理对象上下文CoreData中用于操作和使用数据,负责应用和数据库之间的交互
  1 数据的保存需要NSManagedObjectContext进行save操作
  2 数据的查询需要NSManagedObjectContext进行executeFetchRequest操作(返回值是数组)
  3 CoreData提供的是对象关系映射,NSManagedObjectContext操作的都是NSManagedObject对象
• NSManagedObjectMode:被管理对象对象模型,管理多个对象
• NSManagedObject:被管理对象,CoreData返回的数据模型,被管理的对象是根据实体描述生成的
• NSEntityDescription:实体描述类,根据实体创建被管理对象
• Entity:实体类,实体是对象文件数据的描述,被管理对象表示实体,实体包含名称,属性(字段)和关系,实体的名称通常和被管理对象名一致
• NSFetchRequest:查询请求,NSManagedObjectContext根据NSFetchRequest查询数据,以数组形式返回,数组中包含被管理对象(NSManagedObject)
• NSSortDescriptor:排序操作

CoreData数据库的简单操作

第一步:添加AppDelegate头文件

#import "AppDelegate.h"

第二步:通过单例方法获取协议

AppDelegate *delegate = [UIApplication sharedApplication].delegate;

第三步:创建实体对象

//.创建实体对象(也就是具体对那个表进行操作)
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:delegate.managedObjectContext];

第四步:增删查改

/**增**/
//在创建的时候要使用coreData提供的方法,这样数据管理器就可以管理此数据了
Person *person = [[Person alloc] initWithEntity:entity insertIntoManagedObjectContext:delegate.managedObjectContext];
//同步到数据库
    person.name = @"张三";
    person.sex = @"nan";
    person.age = 12;
    [delegate saveContext];

/**删**/
//    创建请求体
NSFetchRequest *request1 = [[NSFetchRequest alloc] init];
//    //请求需要的具体实体
request1.entity = entity;
//    //创建请求条件
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"age > 1"];
request1.predicate = predicate;
NSArray *array1 = [delegate.managedObjectContext executeFetchRequest:request1 error:nil];
for (Person *person2 in array1) {
    [delegate.managedObjectContext deleteObject:person2];
    NSLog(@"%@",person2.name);
}
[delegate saveContext];

/**查**/
//创建请求体
NSFetchRequest *request = [[NSFetchRequest alloc] init];
//请求体需要的具体实体
request.entity = entity;
NSArray *array = [delegate.managedObjectContext executeFetchRequest:request error:nil];
for (Person *person1 in array) {
    NSLog(@"%@",person1.name);
    NSLog(@"%p",person1);
}

/**改**/
//创建请求体
NSFetchRequest *request2 = [[NSFetchRequest alloc] init];
request2.entity = entity;
//创建请求条件
NSPredicate *predicate1 = [NSPredicate predicateWithFormat:@"name = %@",@"张三"];
request2.predicate = predicate1;
NSArray *array2 = [delegate.managedObjectContext executeFetchRequest:request2 error:nil];
for (Person *person3 in array2) {
    person3.name = @"李四";
    NSLog(@"%@",person3.name);
}
[delegate saveContext];

AppDelegate中CoreData自带的方法

<pre><code>- (NSURL *)applicationDocumentsDirectory {
// The directory the application uses to store the Core Data store file. This code uses a directory named "xalo.UI___CoreData" in the application's documents directory.
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}`
//懒加载

• (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;
  }
  //获取文件目录路径,momd是xcdatamodeld的简写
  NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"UI___CoreData" 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:@"UI___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:@{NSMigratePersistentStoresAutomaticallyOption:@YES,NSInferMappingModelAutomaticallyOption:@YES} 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();
  }
  }
  }