Core Data是ORM框架，很像.NET框架中的EntityFramework。使用的基本步骤是：
- 在项目属性里引入CoreData.framework (标准库)
- 在项目中新建DataModel (生成*.xcdatamodeld文件)
- 在DataModel里创建Entity
- 为Entity生成头文件(菜单Editor/Create NSMangedObject Subclass...)
- 在项目唯一的委托类(AppDelegate.h, AppDelegate.m)里添加managedObjectContext 用来操作Core Data
- 代码任意位置引用 managedObjectContext 读写数据
模型：（注意：myChapter, myContent这些关系都是Cascade,这样删父对象时才会删除子对象）
生成的头文件：
/* Book.h */
@interface Book : NSManagedObject @property (nonatomic, retain) NSNumber * bookId;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSString * author;
@property (nonatomic, retain) NSString * summary;
@property (nonatomic, retain) NSSet *myChapters;
@end @interface Book (CoreDataGeneratedAccessors) - (void)addMyChaptersObject:(NSManagedObject *)value;
- (void)removeMyChaptersObject:(NSManagedObject *)value;
- (void)addMyChapters:(NSSet *)values;
- (void)removeMyChapters:(NSSet *)values; @end /* Chapter.h */
@class Book;
@interface Chapter : NSManagedObject @property (nonatomic, retain) NSNumber * chapId;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSNumber * orderId;
@property (nonatomic, retain) Book *ownerBook;
@property (nonatomic, retain) NSManagedObject *myContent; @end /* TextContent.h */
@class Chapter; @interface TextContent : NSManagedObject @property (nonatomic, retain) NSNumber * chapId;
@property (nonatomic, retain) NSString * text;
@property (nonatomic, retain) Chapter *ownerChapter; @end
委托类代码
AppDelegate.h
// AppDelegate.h #import <UIKit/UIKit.h>
#import <CoreData/CoreData.h> #import "Book.h"
#import "Chapter.h"
#import "TextContent.h" @interface AppDelegate : UIResponder <UIApplicationDelegate> @property (strong, nonatomic) UIWindow *window;
@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext; @end
AppDelegate.m
@implementation AppDelegate
@synthesize managedObjectContext = _managedObjectContext; -(NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil) {
return _managedObjectContext;
} _managedObjectContext = [[NSManagedObjectContext alloc]init]; // 设置数据库路径
NSURL *url = [[[NSFileManager defaultManager]
URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask]lastObject];
NSURL *storeDataBaseURL = [url URLByAppendingPathComponent:@"BOOKS.sqlite"]; // 创建presistentStoreCoordinator
NSError *error = nil;
NSPersistentStoreCoordinator *presistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[NSManagedObjectModel mergedModelFromBundles: nil]]; // 指定存储类型和路径
if (![presistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType
configuration:nil URL:storeDataBaseURL options:nil error:&error]) {
NSLog(@"error : %@", error);
} [_managedObjectContext setPersistentStoreCoordinator: presistentStoreCoordinator];
return _managedObjectContext;
}
使用_managedObjectContext操作Core Data
// 保存新对象
-(void) testStore
{
// 从AppDelegate 获得context
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
NSManagedObjectContext *context = [appDelegate managedObjectContext]; // 第一个章节
TextContent *content1 = [NSEntityDescription insertNewObjectForEntityForName:@"TextContent" inManagedObjectContext:context];
content1.chapId = [NSNumber numberWithInt:];
content1.text = @"hello1"; Chapter *chapter1 = (Chapter *)[NSEntityDescription insertNewObjectForEntityForName:@"Chapter" inManagedObjectContext:context];
chapter1.name = @"hello1";
chapter1.orderId = [NSNumber numberWithInt:];
chapter1.chapId = [NSNumber numberWithInt:];
chapter1.myContent = content1; // 第二个章节
TextContent *content2 = [NSEntityDescription insertNewObjectForEntityForName:@"TextContent" inManagedObjectContext:context];
content2.chapId = [NSNumber numberWithInt:];
content2.text = @"hello2"; Chapter *chapter2 = (Chapter *)[NSEntityDescription insertNewObjectForEntityForName:@"Chapter" inManagedObjectContext:context];
chapter2.name = @"hello2";
chapter2.orderId = [NSNumber numberWithInt:];
chapter2.chapId = [NSNumber numberWithInt:];
chapter2.myContent = content2; // 书籍对象
Book *book = (Book *)[NSEntityDescription insertNewObjectForEntityForName:@"Book" inManagedObjectContext:context];
book.bookId = [NSNumber numberWithInt:];
book.name = @"hello";
book.author = @"Kitty";
book.summary = @"test";
[book addMyChaptersObject:chapter1];
[book addMyChaptersObject:chapter2]; // 提交到持久存储
if ([context hasChanges]) {
[context save:nil];
}
} // 读取对象
-(void) testRead
{
// 从AppDelegate 获得context
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
NSManagedObjectContext *context = [appDelegate managedObjectContext]; // 生成查询对象 （查询全部数据）
NSEntityDescription *entityDescr = [NSEntityDescription entityForName:@"Book" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc]init];
[request setEntity:entityDescr]; // 执行查询
NSError *error;
NSArray *arrayBooks = [context executeFetchRequest:request error:&error]; // 定义排序方式 （根据集合中Chapter对象的orderId属性排序，升序）
NSSortDescriptor *chaptersDescriptor = [NSSortDescriptor sortDescriptorWithKey:@"orderId" ascending:YES]; // 遍历结果集
for (Book *book in arrayBooks) { // 使用当前对象属性
NSLog(@"book name = %@", book.name); // 使用当前对象的集合属性，转成数组
NSArray *arrayChapters = [book.myChapters allObjects]; // 排序
arrayChapters = [arrayChapters
sortedArrayUsingDescriptors:[NSArray arrayWithObjects:chaptersDescriptor,nil]]; // 遍历子数组
for (Chapter *chapter in arrayChapters) {
NSLog(@"chapter name = %@", chapter.name); TextContent *content = (TextContent*) chapter.myContent;
NSLog(@"chapter text = %@", content.text);
}
}
} // 更新对象属性
-(void) testUpdate
{
// 从AppDelegate 获得context
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
NSManagedObjectContext *context = [appDelegate managedObjectContext]; // 生成Request对象
NSEntityDescription *entityDescr = [NSEntityDescription entityForName:@"Book" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc]init];
[request setEntity:entityDescr]; // 执行查询
NSError *error;
NSArray *array = [context executeFetchRequest:request error:&error]; // 更改对象属性
Book * book = array[];
book.name = @"BOOKS"; // 提交到持久存储
if ([context hasChanges]) {
[context save:nil];
}
} // 删除对象
-(void) testRemove
{
// 从AppDelegate 获得context
AppDelegate *appDelegate = [UIApplication sharedApplication].delegate;
NSManagedObjectContext *context = [appDelegate managedObjectContext]; // 生成Request对象
NSEntityDescription *entityDescr = [NSEntityDescription entityForName:@"Book" inManagedObjectContext:context];
NSFetchRequest *request = [[NSFetchRequest alloc]init];
[request setEntity:entityDescr]; // 执行查询
NSError *error;
NSArray *array = [context executeFetchRequest:request error:&error]; // 遍历删除对象,因为在模型里把关系设置为Cascade,所以子对象会被自动删除
for (Book *book in array) {
[context deleteObject:book];
} // 提交到持久存储
if ([context hasChanges]) {
[context save:nil];
}
}