CoreData的學習記錄

1.如果想建立一個帶有coreData的程式,要在項目初始化的時候勾選中

2.建立完成之後,會發現在AppDelegate裡多出了幾個屬性,和2個方法

@property (readonly, strong, nonatomic) NSManagedObjectContext *managedObjectContext;@property (readonly, strong, nonatomic) NSManagedObjectModel *managedObjectModel;@property (readonly, strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;- (void)saveContext;- (NSURL *)applicationDocumentsDirectory;

managedObjectContext （被管理的資料內容）操作實際內容（操作持久層）作用：插入資料，查詢資料，刪除資料

NSManagedObjectModel（被管理的資料模型）資料庫所有表格或資料結構，包含各實體的定義資訊 作用：添加實體的屬性，建立屬性之間的關係操作方法：視圖編輯器，或代碼

NSPersistentStoreCoordinator（持久化儲存助理）相當於資料庫的連接器 作用：設定資料存放區的名字，位置，儲存方式，和儲存時機

方法saveContext表示：儲存資料到持久層（資料庫）

方法applicationDocumentsDirectory表示：應用程式沙箱下的Documents目錄路徑

3.如果想建立一個實體物件的話,需要點擊.xcdatamodel,Add Entity,添加想要的欄位

4.產生對象檔案,command+n,然後選中CoreData裡的NSManagerObjectSubClass進行關聯,選中實體建立

5.添加資料

Person *newPerson = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:self.managedObjectContext];        if (newPerson == nil){        NSLog(@"Failed to create the new person.");        return NO;    }        newPerson.firstName = paramFirstName;    newPerson.lastName = paramLastName;    newPerson.age = [NSNumber numberWithUnsignedInteger:paramAge];    NSError *savingError = nil;        if ([self.managedObjectContext save:&savingError]){        return YES;    } else {        NSLog(@"Failed to save the new person. Error = %@", savingError);    }

NSEntityDescription（實體結構）相當於表格結構

6.取出資料查詢

/* Create the fetch request first */    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];    /* Here is the entity whose contents we want to read */    NSEntityDescription *entity =    [NSEntityDescription     entityForName:@"Person"     inManagedObjectContext:self.managedObjectContext];    /* Tell the request that we want to read the     contents of the Person entity */    [fetchRequest setEntity:entity];    NSError *requestError = nil;    /* And execute the fetch request on the context */    NSArray *persons =    [self.managedObjectContext executeFetchRequest:fetchRequest                                             error:&requestError];    /* Make sure we get the array */    if ([persons count] > 0){        /* Go through the persons array one by one */        NSUInteger counter = 1;        for (Person *thisPerson in persons){            NSLog(@"Person %lu First Name = %@",                  (unsigned long)counter,                   thisPerson.firstName);             NSLog(@"Person %lu Last Name = %@",                   (unsigned long)counter,                   thisPerson.lastName);            NSLog(@"Person %lu Age = %ld",                  (unsigned long)counter,                  (unsigned long)[thisPerson.age unsignedIntegerValue]);            counter++;        }    } else {        NSLog(@"Could not find any Person entities in the context.");     }

7.刪除資料

/* Create the fetch request first */    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];    /* Here is the entity whose contents we want to read */    NSEntityDescription *entity =    [NSEntityDescription     entityForName:@"Person"     inManagedObjectContext:self.managedObjectContext];    /* Tell the request that we want to read the     contents of the Person entity */    [fetchRequest setEntity:entity];    NSError *requestError = nil;    /* And execute the fetch request on the context */    NSArray *persons =    [self.managedObjectContext executeFetchRequest:fetchRequest                                             error:&requestError];    if ([persons count] > 0){        /* Delete the last person in the array */        Person *lastPerson = [persons lastObject];        [self.managedObjectContext deleteObject:lastPerson];        NSError *savingError = nil;        if ([self.managedObjectContext save:&savingError]){            NSLog(@"Successfully deleted the last person in the array.");        } else {            NSLog(@"Failed to delete the last person in the array.");        }    } else {         NSLog(@"Could not find any Person entities in the context.");     } 

8.排序

//排序    NSSortDescriptor *ageSort = [[NSSortDescriptor alloc]initWithKey:@"age" ascending:YES];    NSSortDescriptor *firstNameSort =    [[NSSortDescriptor alloc] initWithKey:@"firstName"                                ascending:YES];    NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:                                ageSort,firstNameSort,  nil];    fetchRequest.sortDescriptors = sortDescriptors;

注意: ascending:YES 是區分排序的

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如果之前的工程裡並沒有引入coreData,我們則可以加入CoreData.FrameWork,然後command+N 

建立一個.xcdatamodel,並實現如下代碼

@property (nonatomic, retain) NSManagedObjectModel *managedObjectModel;  @property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;  @property (nonatomic, retain) NSPersistentStoreCoordinator *persistentStoreCoordinator;

#pragma mark - #pragma mark - Core Data Stack- (NSManagedObjectModel *)managedObjectModel{    if (nil != _managedObjectModel) {        return _managedObjectModel;    }        _managedObjectModel = [[NSManagedObjectModel mergedModelFromBundles:nil] retain];    return _managedObjectModel;}- (NSManagedObjectContext *)managedObjectContext{    if (nil != _managedObjectContext) {        return _managedObjectContext;    }        _managedObjectContext = [[NSManagedObjectContext alloc] init];        if (self.persistentStoreCoordinator) {        [_managedObjectContext setPersistentStoreCoordinator:self.persistentStoreCoordinator];    }        return _managedObjectContext;}- (NSPersistentStoreCoordinator *)persistentStoreCoordinator{    if (nil != _persistentStoreCoordinator) {        return _persistentStoreCoordinator;    }        NSString *storeType = NSSQLiteStoreType;    NSString *storeName = @"cdNBA.sqlite";        NSError *error = NULL;    NSURL *storeURL = [NSURL fileURLWithPath:[[self applicationDocumentsDirectory] stringByAppendingPathComponent:storeName]];        _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:self.managedObjectModel];    if (![_persistentStoreCoordinator addPersistentStoreWithType:storeType configuration:nilURL:storeURL options:nil error:&error]) {        NSLog(@"Error : %@\n", [error localizedDescription]);        NSAssert1(YES, @"Failed to create store %@ with NSSQLiteStoreType", [storeURL path]);    }        return _persistentStoreCoordinator;}#pragma mark -#pragma mark Application's Documents Directory- (NSString *)applicationDocumentsDirectory{    NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);    NSString *basePath = ([paths count] > 0) ? [paths objectAtIndex:0] : nil;    return basePath;}

我們每一次儲存的時候都要調用一下managedObjectContext的save方法,因為在context中建立的對象只是存在於記憶體中,所以我們要實際把他儲存在sqlite裡面,得到applicationDocumentsDirectory方法裡的url,到前往->前往檔案夾裡可以看到你建立的sqlite