核心数据关系不是零，但返回零对象

Question

我有实体：

@class CDCustomItem;

@interface CDCustomItem : NSManagedObject

@property (nonatomic, retain) CDCustomImage *image;
@end

和CDCustomImage实体：

@class CDCustomImage;

@interface CDCustomImage : NSManagedObject

@property (nonatomic, retain) NSString * url;
@property (nonatomic, retain) CDCustomItem *itemParent;

@end

CDCustomImage.image和CDCustomImage.itemParent的类型为“To One”

将图像插入CDCustomItem后，它会显示在NSLog：

中

image = "0x79e59df0 <x-coredata:///CDCustomImage/t765B46F3-87B1-4C09-A108-6584F4E58DDB214>";

但是当我尝试NSLog(@"%@", CDCustomItem.image)时，它会返回null

为什么会这样？怎么解决？请帮忙

编辑1： 所有操作都在一个线程中

编辑2： 以下是如何将图像插入CDCustomItem的代码：

CDCustomImage *image = [self insertImage:[jsonDict objectForKey:@"image"]];
item.image = image;

- (CDCustomImage *)insertImage:(NSDictionary *)jsonDict {
    CDCustomImage *entity = [self insertEntityWithName:[CDCustomImage description]];
    [self fillFieldsForImage:entity dict:jsonDict];

    return entity;
}

- (void)fillFieldsForImage:(CDCustomImage *)entity dict:(NSDictionary *)jsonDict {
    entity.url = [jsonDict valueForKey:@"url"];
}