Core data NSManagedObject自定义类--NSInvalidArgumentException无法识别的选择器--

我有一个定制的NSManagedObject类，看起来像这样

#import <Foundation/Foundation.h>
#import <CoreData/CoreData.h>

@class Ingredient, MenuCategory, Price, ItemSize;

@interface Item : NSManagedObject

@property (nonatomic, retain) NSNumber * collected;
@property (nonatomic, retain) NSString * desc;
@property (nonatomic, retain) NSString * instructions;
@property (nonatomic, retain) NSString * name;
@property (nonatomic, retain) NSNumber * quantity;
@property (nonatomic, retain) NSNumber * selected;
@property (nonatomic, retain) MenuCategory *menuCategory;
@property (nonatomic, retain) NSSet *prices;
@property (nonatomic, retain) NSSet *itemSizes;
@property (nonatomic, retain) NSSet *itemIngredients;


-(NSMutableSet *)mutablePrices;
-(NSMutableSet *)mutableItemIngredients;

@end

#import "Item.h"
#import "Ingredient.h"
#import "MenuCategory.h"
#import "Price.h"
#import "ItemSize.h"


@implementation Item

@dynamic collected;
@dynamic desc;
@dynamic instructions;
@dynamic name;
@dynamic quantity;
@dynamic selected;
@dynamic itemIngredients;
@dynamic menuCategory;
@dynamic prices;
@dynamic itemSizes;


-(NSMutableSet *)mutablePrices{

    return [self mutableSetValueForKey:@"prices"];
}

-(NSMutableSet *)mutableItemIngredients{

    return [self mutableSetValueForKey:@"itemIngredients"];
}

@end

但它并没有给我以下的错误

2014-03-30 10:25:34.594 restos[1192:60b] -[NSManagedObject mutablePrices]: unrecognized selector sent to instance 0xe8d72c0
2014-03-30 10:25:34.597 restos[1192:60b] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[NSManagedObject mutablePrices]: unrecognized selector sent to instance 0xe8d72c0'

但当我做以下事情时

[[item mutableSetValueForKey:@"prices"] addObject:newPrice];

很好用——我知道有些东西很简单，因为某种原因我看不见----

提前感谢您

错误消息

-[NSManagedObject mutablePrices]: unrecognized selector sent to instance 0xe8d72c0

指示您的

项

对象不是

项

类的实例。一个可能的原因可能是您没有在核心数据中将实体的类设置为“Item” 模特检查员

通常，如果让Xcode生成NSManagedObject子类文件（从“编辑”菜单），并在类类别中添加自定义方法，则不太容易出错。或者，使用

-[NSManagedObject mutablePrices]: unrecognized selector sent to instance 0xe8d72c0