iphone - CoreData关系澄清: How to effectively set an inverse relationship

Question

我的 CoreData 关系设置如下:(抱歉，我是 stackoverflow 的新手，所以我必须用 ascii 来绘制它)。

<小时/>

故事(对象)

• 属性:创建日期，订单，

• 关系:句子(一对多与句子)

句子(宾语)

• 属性:图像、顺序、文本

• 关系:belongsTo(与故事一对一)

<小时/>

注释:

• 句子关系是一个 NSSet
• belongsTo 关系是一个故事

简单来说，一个Story有很多Sentence，但一个Sentence只能属于一个Story。

我在有效设置belongsTo属性时遇到了麻烦 - 而且我知道我有点缺少范例。我担心当我设置 ownTo 时，我将使用它自己的 NSSet 创建另一个 Story 对象，从而创建一个递归循环。无论如何，我的问题似乎是有效设置每个句子的belongsTo 属性/关系。

将我的数据插入 CoreData 存储库的代码如下所示:

-(void)addStoryItemAction:(Sentence*)sentence{

[self dismissModalViewControllerAnimated:YES];  
Story *story = [[Story alloc] initWithSentence: sentence];

sentence.belongsTo = story;

//crash and burn here.

Story *storySetter = (Story*)   [NSEntityDescription insertNewObjectForEntityForName:@"Story" inManagedObjectContext:managedObjectContext];
[storySetter setSentences:      story.sentences];
[storySetter setCreationDate:   story.creationDate];
[storySetter setOrder:          story.order];

NSError *error;  

BOOL isSaved = [managedObjectContext save:&error];
NSLog(@"isSaved? %@", (isSaved ? @"YES" :@"NO ") );

if (!isSaved) {
    NSLog(@"%@:%s Error saving context: %@", [self class], _cmd, [error localizedDescription]);
    return;
}

}

运行时出现以下错误:

-[Sentence setBelongsTo:]:无法识别的选择器发送到实例 0x5b5aa00

我知道我在某个地方错过了重点 - 有人可以澄清我出错的地方，以便我可以有效地实现此 CoreData 集的插入吗？

仅供引用:句子.h:

 #import <Foundation/Foundation.h>
 #import "Story.h"

 @class Story;

 @interface Sentence : NSManagedObject {
 }
 @property (assign) NSString  *text;
 @property (assign) NSString  *image;
 @property (assign) NSInteger *order;
 @property (nonatomic, retain) Story  *belongsTo;

 - (id)initWithContent:(NSString*)sentenceText image:(NSString*)sentenceImage order: (NSInteger*)sentencePosition;
 @end

句子.m:

 #import "Sentence.h"
 @implementation Sentence
 @synthesize text;
 @synthesize image;
 @synthesize order;
 @dynamic belongsTo;

 - (id)initWithContent:(NSString*)sentenceText image:(NSString*)sentenceImage order: (NSInteger*)sentencePosition{
[self setText:  sentenceText];
[self setImage: sentenceImage];
[self setOrder: sentencePosition];  
return self;
 }
 @end

故事.h

 #import <Foundation/Foundation.h>
 #import <CoreData/CoreData.h>
 #import "Sentence.h" 
 @class Sentence;
 @interface Story : NSManagedObject {
 }
 @property (assign) NSSet     *sentences;
 @property (assign) NSDate    *creationDate;
 @property (assign) NSInteger *order;

 - (id)initWithSentence:(Sentence*)sentence;
 @end

故事.m

 #import "Story.h"
 @implementation Story
 @synthesize sentences;
 @synthesize creationDate;
 @synthesize order;

 - (id)initWithSentence: (Sentence*) sentence{

NSLog(@"initWithSencence: sentence: %@", sentence);
sentences = [[NSSet alloc] initWithObjects:sentence, nil];
//[sentences setByAddingObject:sentence];
[self setSentences:sentences];
NSLog(@"sentences (in story object): %@", sentences);
creationDate = [NSDate date];
[self setCreationDate:creationDate];
//later expansion, position should be max(position of all stories) ++
[self setOrder:0];

 return self;
 }

 @end

Answer 1

我有点困惑为什么你直接在 Story 上调用 alloc/init 。我怀疑，如果您在代码中的其他地方做同样的事情(您应该发布给我们看)，那么传递给 addStoryItemAction: 的“句子”对象可能不是正确初始化的 NSManagedObject。

您遇到的错误意味着底层类没有正确实现该属性“belongsTo”的访问器，因此您的初始化代码中似乎出现了问题。您应该使用:

NSEntityDescription *entityFromModel = [[aModel entitiesByName] valueForKey:@"Sentence"];
Sentence *sentence = (Sentence *)[[NSManagedObject alloc] initWithEntity:entityFromModel insertIntoManagedObjectContext:context];