iOS: Core Data入门

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:100];

    content1.text = @"hello1";

    

    Chapter *chapter1 = (Chapter *)[NSEntityDescription insertNewObjectForEntityForName:@"Chapter" inManagedObjectContext:context];

    chapter1.name = @"hello1";

    chapter1.orderId = [NSNumber numberWithInt:0];

    chapter1.chapId =  [NSNumber numberWithInt:100];

    chapter1.myContent = content1;

    

    // 第二个章节

    TextContent *content2 = [NSEntityDescription insertNewObjectForEntityForName:@"TextContent" inManagedObjectContext:context];

    content2.chapId = [NSNumber numberWithInt:100];

    content2.text = @"hello2";

    

    Chapter *chapter2 = (Chapter *)[NSEntityDescription insertNewObjectForEntityForName:@"Chapter" inManagedObjectContext:context];

    chapter2.name = @"hello2";

    chapter2.orderId = [NSNumber numberWithInt:1];

    chapter2.chapId =  [NSNumber numberWithInt:101];

    chapter2.myContent = content2;

    

    // 书籍对象

    Book *book = (Book *)[NSEntityDescription insertNewObjectForEntityForName:@"Book" inManagedObjectContext:context];

    book.bookId = [NSNumber numberWithInt:100];

    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[0];

    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];

    }

}