学步园

文中代码均来源于：http://www.appcoda.com/introduction-to-core-data/

希望学习 Core Data 的同学不要错过：）以下是我个人记录的一些常用代码片段。

有一个 Entity：Device，有三个属性：company、name、version。

1.获取 context 的方法：

- (NSManagedObjectContext *)managedObjectContext {
    NSManagedObjectContext *context = nil;
    id delegate = [[UIApplication sharedApplication] delegate];
    if ([delegate performSelector:@selector(managedObjectContext)]) {
        context = [delegate managedObjectContext];
    }
    return context;
}

2.增加一条数据：

    NSManagedObjectContext *context = [self managedObjectContext];
    
    // Create a new managed object
    NSManagedObject *newDevice = [NSEntityDescription insertNewObjectForEntityForName:@"Device" inManagedObjectContext:context];
    [newDevice setValue:self.nameTextField.text forKey:@"name"];
    [newDevice setValue:self.versionTextField.text forKey:@"version"];
    [newDevice setValue:self.companyTextField.text forKey:@"company"];
    
    NSError *error = nil;
    // Save the object to persistent store
    if (![context save:&error]) {
        NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
    }

3.删除一条数据：

NSManagedObjectContext *context = [self managedObjectContext];

// Delete object from database
[context deleteObject:[self.devices objectAtIndex:indexPath.row]];

NSError *error = nil;
if (![context save:&error]) {
    NSLog(@"Can't Delete! %@ %@", error, [error localizedDescription]);
    return;
}

4.修改一条数据：

NSManagedObjectContext *context = [self managedObjectContext];
    
// Update existing device
[self.device setValue:self.nameTextField.text forKey:@"name"];
[self.device setValue:self.versionTextField.text forKey:@"version"];
[self.device setValue:self.companyTextField.text forKey:@"company"];


NSError *error = nil;
// Save the object to persistent store
if (![context save:&error]) {
    NSLog(@"Can't Save! %@ %@", error, [error localizedDescription]);
}

5. 查询一堆数据：

// Fetch the devices from persistent data store
NSManagedObjectContext *managedObjectContext = [self managedObjectContext];
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Device"];
self.devices = [[managedObjectContext executeFetchRequest:fetchRequest error:nil] mutableCopy];