macos Core Data 中多对多关系的属性声明

Property declaration for to-many relationships in Core Data

提问by hekevintran

I have an application written using Core Data. I have 2 entities with a one-to-many relationship. I have subclassed NSManagedObject for both of them. The entity on the one-side is called Playlist and the other is called Song.

我有一个使用 Core Data 编写的应用程序。我有 2 个具有一对多关系的实体。我已经为他们两个子类化了 NSManagedObject。一侧的实体称为播放列表，另一侧的实体称为歌曲。

The interface for Playlist:

播放列表界面：

@interface VBPlaylist : NSManagedObject {
}

@property (readwrite, copy) NSString *name;

@end

The implementation for Playlist:

播放列表的实现：

@implementation VBPlaylist

@dynamic name;

@end

I think that I should have another property to indicate the Songs under the Playlist class. I cannot find any sample code that shows to-many relationships written as properties. How do you do this?

我认为我应该有另一个属性来指示播放列表类下的歌曲。我找不到任何显示编写为属性的多对关系的示例代码。你怎么做到这一点？

回答by Barry Wark

To-one relationships are modeled as object references by Core Data. So a to-one relationship from Entity Barto entity Baz(assuming Bazis implemented by the class Baz) would be

一对一关系被 Core Data 建模为对象引用。所以从实体Bar到实体的一对一关系Baz（假设Baz是由类实现的Baz）将是

@interface Bar : NSManagedObject {
}

@property (readwrite,nonatomic) Baz * toBaz;

@end

To-many relationships are modeled as a mutable set property (though notas an NSMutableSet). Assuming a to-many relationship from Barto Bazcalled manyBazz:

对多关系被建模为一个可变的集合属性（虽然不是一个NSMutableSet）。假设从Bar到Baz被调用的一对多关系manyBazz：

@interface Bar : NSManagedObject {

}

@property (retain) NSSet* manyBazz;

@end

// coalesce these into one @interface AnalysisRecord (CoreDataGeneratedAccessors) section
@interface Bar (CoreDataGeneratedAccessors)
- (void)addManyBazzObject:(Baz *)value;
- (void)removeManyBazzObject:(Baz *)value;
- (void)addManyBazz:(NSSet *)value;
- (void)removeManyBazz:(NSSet *)value;

@end

If you want to use the NSMutableSet interface to manipulate the manyBazzrelationship, you should call -mutableSetValueForKey:@"manyBazz"to get a KVO-compliant proxy for the manyBazzrelationship.

如果您想使用 NSMutableSet 接口来操作manyBazz关系，您应该调用-mutableSetValueForKey:@"manyBazz"以获取该manyBazz关系的 KVO 兼容代理。

On Leopard (OS X 10.5) and later, all appropriate methods are automaticall generated at run-time by the Core Data framework, even if you do not explicitly declare or implement them (you will, of course, get a compiler warning if you try to use them without declaring them in a header file). Thus you do not needto subclass

在 Leopard (OS X 10.5) 及更高版本上，所有适当的方法都会在运行时由 Core Data 框架自动生成，即使您没有明确声明或实现它们（当然，如果您尝试，您将收到编译器警告使用它们而不在头文件中声明它们）。因此你不需要子类化

The easiest way to get the declaration and implementation right is to select the attributes in the data modeler and choose "Copy Objective-C 2.0 Method Declarations To Clipboard" from the "Design->Data Model" menu, the paste into your implementing classes .h file. Of course, you have to keep your .h and model in sync... hence a hearty recommendation for rentzsch's awesome MO Generator, a tool that will automatically generate (and re-generate) NSManagedObject subclasses from your data model.

获得正确声明和实现的最简单方法是在数据建模器中选择属性，然后从“设计->数据模型”菜单中选择“将 Objective-C 2.0 方法声明复制到剪贴板”，粘贴到您的实现类中。 h文件。当然，你必须让你的 .h 和模型保持同步......因此强烈推荐rentzsch的很棒的MO Generator，这是一个从你的数据模型自动生成（和重新生成） NSManagedObject 子类的工具。

回答by Jim Dovey

The simplest way to create .h and .m files for your CoreData entities is this:

为 CoreData 实体创建 .h 和 .m 文件的最简单方法是：

1. Select an entity in the data modeler.
2. Press Command-N or select File->New File…
3. Select 'Cocoa' from the source list.
4. In the template chooser, you should now see an item called 'Managed Object Class'. If this isn't there, click Cancel and repeat steps 1-2.
5. Press Next, choose the project/target, and press Next again.
6. Now you see something like the following window: New Managed Object Class window http://blog.alanquatermain.net/images/ManagedObjectClass.png
7. Select the options you need and click Finish.

1. 在数据建模器中选择一个实体。
2. 按 Command-N 或选择 File->New File…
3. 从源列表中选择“可可”。
4. 在模板选择器中，您现在应该看到一个名为“Managed Object Class”的项目。如果不存在，请单击取消并重复步骤 1-2。
5. 按 Next，选择项目/目标，然后再次按 Next。
6. 现在您会看到类似于以下窗口的内容：New Managed Object Class window http://blog.alanquatermain.net/images/ManagedObjectClass.png
7. 选择您需要的选项并单击完成。

This will generate the following header and source files:

这将生成以下头文件和源文件：

Entity.h:

实体.h：

#import <CoreData/CoreData.h>


@interface Entity :  NSManagedObject  
{
}

@property (retain) NSNumber * uniqueID;
@property (retain) NSString * name;
@property (retain) Entity * parent;
@property (retain) NSSet* children;

@end

@interface Entity (CoreDataGeneratedAccessors)
- (void)addChildrenObject:(Entity *)value;
- (void)removeChildrenObject:(Entity *)value;
- (void)addChildren:(NSSet *)value;
- (void)removeChildren:(NSSet *)value;

@end

Entity.m:

实体.m：

#import "Entity.h"


@implementation Entity 

@dynamic uniqueID;
@dynamic name;
@dynamic parent;
@dynamic children;

@end

Note that the implementation doesn't contain anything except @dynamicmarkers to tell the compiler not to worry about missing methods/variables to match the properties.

请注意，除了@dynamic告诉编译器不要担心缺少方法/变量来匹配属性的标记之外，该实现不包含任何内容。

回答by DRVic

This has slightly changed. As of 4.2.1 (March 2012), you go to New File; select Core Data (not Cocoa), and then select New NSObjectModel subclass. From there it produces the subclass as described above.

这略有改变。从 4.2.1（2012 年 3 月）开始，您转到新建文件；选择 Core Data (not Cocoa)，然后选择 New NSObjectModel subclass。从那里它产生如上所述的子类。