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使用CoreData [1]

2024-07-14 21:12:12   225人阅读

使用CoreData [1]

本篇教程能教你从无开始接触CoreData,包括新建工程,创建出实体,增删改查样样都有,属于使用CoreData最初级教程.

 

1. 创建带有CoreData的工程项目

 

2. 添加一个实体类

 

3. 创建出实体类

 

4. 创建对象,保存对象,执行代码

以下是验证结果:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    NSLog(@"%@", NSHomeDirectory());        // 实体描述信息    NSEntityDescription *description =         [NSEntityDescription entityForName:@"Student"                    inManagedObjectContext:[self managedObjectContext]];        // 初始化对象    Student *student = [[Student alloc] initWithEntity:description                        insertIntoManagedObjectContext:[self managedObjectContext]];    student.name     = @"YouXianMing";    student.age      = [NSNumber numberWithInt:26];        // 保存对象    [self saveContext];    return YES;}

这样就实现了存储对象.

 

5. 重复上面的步骤存储5个对象.

 

6. 遍历出所有的对象

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    // 设定要查询的实体    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];        // 取出查询结果    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];        // 遍历    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;        NSLog(@"%@ %@", student.age, student.name);    }];    return YES;}

 

7. 删除一个对象

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    // 设定要查询的实体    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];        // 取出查询结果    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];        // 遍历    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;        // 找到匹配的数据,删除之        if ([student.name isEqualToString:@"QiuLiang"])        {            [[self managedObjectContext] deleteObject:student];        }    }];        // 存储    [self saveContext];        // 遍历    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;                NSLog(@"%@ %@", student.age, student.name);    }];    return YES;}

 

8. 修改一个对象

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions{    // 设定要查询的实体    NSFetchRequest *fetch = [NSFetchRequest fetchRequestWithEntityName:@"Student"];        // 取出查询结果    NSArray *students = [[self managedObjectContext] executeFetchRequest:fetch error:nil];        // 遍历    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;        // 找到匹配的数据,修改之        if ([student.name isEqualToString:@"YouXianMing"])        {            student.age = [NSNumber numberWithInt:100];        }    }];        // 存储    [self saveContext];        // 遍历    [students enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop) {        Student *student = obj;                NSLog(@"%@ %@", student.age, student.name);    }];    return YES;}

 

9. 根据谓词查找出实体的方法请自行百度脑补,这里不赘述了.

 


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