iOS持久化Core Data之一 CoreDataHelper

说明：按照《Core Data 应用开发》的思路整理记录

(一) 创建 CoreDataHelper

|-------------------------------|       |------------------|        |--------------------------------|

|   持久化存储协调器     |       |托管对象模型|        |      托管对象context       |

|-------------------------------|       |------------------|        |--------------------------------|

|      持久化存储区         |       |      对象图     |        |                                       |

|     数据表中的某行 <=======================>  托管对象                |

|__________________|       |___________|         |___________________|

1 持久化存储协调器 persistent store coordinator

    NSPersistentStore : 用于创建持久化存储区

    NSPersistentStoreCoordinator : 用于创建持久化存储协调器

2 托管对象模型（对象图）

    NSManagedObjectModel : 用于创建托管对象模型

3 托管对象上下文

    NSManagedObjectContext : 创建托管对象上下文

CoreDataHelper.h

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@interface CoreDataHelper : NSObject

@property(nonatomic,readonly) NSManagedObjectContext *context;  //上下文
@property(nonatomic,readonly) NSManagedObjectModel *model;  //托管对象模型
@property(nonatomic,readonly) NSPersistentStoreCoordinator *coordinator;    //持久化存储协调器
@property(nonatomic,readonly) NSPersistentStore *store; //持久化存储区

- (void)setupCoreData;  //设置
- (void)saveContext;    //将 _context 中的改变保存在 _store 中

@end

CoreDataHelper.m

#import "CoreDataHelper.h"

@implementation CoreDataHelper

//调试输出
#define debug 1

#pragma mark - FILES
//持久化真实存储文件名
NSString *storeFilename = @"Grocery-Dude.sqlite";

#pragma mark - PATHS
//获取沙盒 Documents 的路径
- (NSString *)applicationDocumentsDirectory{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}
//创建 Documents 下文件夹 Stores
- (NSURL *)applicationStoresDirectory{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    
    NSURL *storesDirectory = [[NSURL fileURLWithPath:[self applicationDocumentsDirectory]] URLByAppendingPathComponent:@"Stores"];
    
    NSFileManager *filemanager = [NSFileManager defaultManager];
    if(![filemanager fileExistsAtPath:[storesDirectory path]]){
        NSError *error = nil;
        if([filemanager createDirectoryAtURL:storesDirectory withIntermediateDirectories:YES attributes:nil error:&error]){
            if(debug == 1){
                NSLog(@"Successfully created Stores directory");
            }
        }else{
            NSLog(@"Failed to create Stores directory: %@",error);
        }
    }
    return storesDirectory;
}
//给 url 拼接最后的文件名 Grocery-Dude.sqlite
- (NSURL *)storeURL{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    return [[self applicationStoresDirectory] URLByAppendingPathComponent:storeFilename];
}

#pragma mark - SETUP
- (id)init{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    self = [super init];
    if(!self){
        return nil;
    }
    
    //根据对象图创建对象模型
    _model = [NSManagedObjectModel mergedModelFromBundles:nil];
    //根据对象模型创建持久化协调器
    _coordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:_model];
    //创建某type型的上下文
    _context = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    //上下文和协调器连接
    [_context setPersistentStoreCoordinator:_coordinator];
    return self;
}
//加载sqlite持久化文件
- (void)loadStore{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    
    if(_store){return;}
    NSError *error = nil;
    _store = [_coordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:[self storeURL] options:nil error:&error];
}
- (void)setupCoreData{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    [self loadStore];
}

#pragma mark - SAVING
//将 _context 中的改变保存在 _store 中
- (void)saveContext{
    if(debug == 1){
        NSLog(@"Running %@ '%@'", self.class,NSStringFromSelector(_cmd));
    }
    
    if([_context hasChanges]){
        NSError *error = nil;
        if([_context save:&error]){
            NSLog(@"_context SAVED changes to persistent store");
        }else{
            NSLog(@"Failed to save _context: %@", error);
        }
    }else{
        NSLog(@"SKIPPED _context save, there are no changes!");
    }
}

@end

(二) 创建托管对象模型 Data Model

(三) 生成 NSManagedObject

1.手动生成

对应的对象图：

对应的Code：

TestCD.h

#import <CoreData/CoreData.h>

@interface TestCD : NSManagedObject

@property(nonatomic,copy) NSString *name;

@end

TestCD.m

#import "TestCD.h"

@implementation TestCD

@dynamic name;

@end

  这里用了 dynamic 关键字，因为 Core Data 在运行的时候会自动生成属性的存取方法

  当属性多时，我们可以用nonnull和nullable等修饰属性，让属性是否可以为空

  我们还可以加个类方法：

+ (NSFetchRequest *)fetchRequest {
    return [[NSFetchRequest alloc] initWithEntityName:@"Test"];
}

(四) 存储

    NSArray *arrayObjs = @[@"Milk", @"Apples", @"Bread", @"Cheese", @"Orange Juice"];
    for(NSString *name in arrayObjs){
        TestCD *test = [NSEntityDescription insertNewObjectForEntityForName:@"Test" inManagedObjectContext:_coreDataHelper.context];
        test.name = name;
    }
    [_coreDataHelper saveContext];

(五) 排序获取

//    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Test"];
    NSFetchRequest *request = [TestCD fetchRequest];
    NSSortDescriptor *sort = [NSSortDescriptor sortDescriptorWithKey:@"name" ascending:YES];
    [request setSortDescriptors:[NSArray arrayWithObject:sort]];
    
    NSArray *fetchedObjects = [_coreDataHelper.context executeFetchRequest:request error:nil];
    for(TestCD *item in fetchedObjects){
        NSLog(@"Fetched Object = %@", item.name);
    }

(六) 筛选/删除

筛选用到谓词  NSPredicate 

    NSPredicate *filter = [NSPredicate predicateWithFormat:@"name = %@", @"Milk"];
    NSFetchRequest *request = [NSFetchRequest fetchRequestWithEntityName:@"Test"];
    [request setPredicate:filter];
    NSArray *fetchedObjects = [_coreDataHelper.context executeFetchRequest:request error:nil];
    for(TestCD *test in fetchedObjects){
        NSLog(@"Fetched Object = %@", test.name);
    }

获取请求模板：

在对象图上使用 FETCH REQUESTS 

删除托管对象：

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

    NSArray *fetchedObjects = [_coreDataHelper.context executeFetchRequest:request error:nil];
    for(TestCD *test in fetchedObjects){
        NSLog(@"Fetched Object = %@", test.name);
        [_coreDataHelper.context deleteObject:test];
    }
    
    [_coreDataHelper saveContext];