Core data 核心数据自定义类未知链接器错误

伙计们，我一直在引用这个项目，但我得到了这个链接器错误：

Undefined symbols:
  "_OBJC_CLASS_$_NSManagedObject", referenced from:
      _OBJC_CLASS_$_ParkingLot in ParkingLot.o
      _OBJC_CLASS_$_Permit in Permit.o
  "_OBJC_METACLASS_$_NSManagedObject", referenced from:
      _OBJC_METACLASS_$_ParkingLot in ParkingLot.o
      _OBJC_METACLASS_$_Permit in Permit.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

以下是我编写的相关代码[向下滚动到自定义托管对象类]：

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

@class ParkingLot;

@interface Permit :  NSManagedObject  
{
}

@property (nonatomic, retain) NSString * eligibility;
@property (nonatomic, retain) NSString * pricing;
@property (nonatomic, retain) NSString * type;
@property (nonatomic, retain) NSString * summary;
@property (nonatomic, retain) NSString * timeValid;
@property (nonatomic, retain) NSSet* parkingLots;

@end


@interface Permit (CoreDataGeneratedAccessors)
- (void)addParkingLotsObject:(ParkingLot *)value;
- (void)removeParkingLotsObject:(ParkingLot *)value;
- (void)addParkingLots:(NSSet *)value;
- (void)removeParkingLots:(NSSet *)value;

@end

//Permit.m
#import "Permit.h"

#import "ParkingLot.h"

@implementation Permit 

@dynamic eligibility;
@dynamic pricing;
@dynamic type;
@dynamic summary;
@dynamic timeValid;
@dynamic parkingLots;

@end

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


@interface ParkingLot :  NSManagedObject  
{
}

@property (nonatomic, retain) NSString *title;
@property (nonatomic, retain) id region;
@property (nonatomic, retain) NSSet* permits;

@end


@interface ParkingLot (CoreDataGeneratedAccessors)
- (void)addPermitsObject:(NSManagedObject *)value;
- (void)removePermitsObject:(NSManagedObject *)value;
- (void)addPermits:(NSSet *)value;
- (void)removePermits:(NSSet *)value;

@end

//ParkingLot.m
#import "ParkingLot.h"


@implementation ParkingLot 

@dynamic title;
@dynamic region;
@dynamic permits;

@end

---

如果你看一下我遵循的示例代码，它几乎是相同的，但它拒绝工作，我不明白为什么。提前感谢您的帮助

愚蠢的我。。。我需要将核心数据框架添加到我的项目中。我可以发誓我已经这么做了。。。这就是我在凌晨编程的收获。

愚蠢的我。。。我需要将核心数据框架添加到我的项目中。我可以发誓我已经这么做了。。。这就是我在凌晨编程的结果。

我犯了同样的错误+我犯了同样的错误+1用于简单、明显的解决方案。