Question

I have a cocoa-touch app, using the core data framework.

I’ve created a xcdatamodel with two entities: Program and ProgramReplay.
ProgramReplay has a relationship to Program, and a reverse relationship exists in the later.

I’ve saved this, and used XCode’s feature to generate the classes for these two entities. The generated headers are as follows:

#import <CoreData/CoreData.h>
@class ProgramReplay;
@interface Program :  NSManagedObject  
{
}

// other properties here, removed them to keep it short
@property (nonatomic, retain) NSSet* replays;
@end

@interface Program (CoreDataGeneratedAccessors)
- (void)addReplaysObject:(ProgramReplay *)value;
- (void)removeReplaysObject:(ProgramReplay *)value;
- (void)addReplays:(NSSet *)value;
- (void)removeReplays:(NSSet *)value;
@end

and

#import <CoreData/CoreData.h>
@class Program;
@interface ProgramReplay :  NSManagedObject  
{
}

@property (nonatomic, retain) NSDate * date;
@property (nonatomic, retain) Program * program;
@end

I haven’t started using these two classes anywhere yet, but when I try to build them I get the following weird linking errors:
".objc_class_name_NSManagedObject", referenced from:
.objc_class_name_Program in Program.o
.objc_class_name_ProgramReplay in ProgramReplay.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

What am I doing wrong?

Answer 1

It looks like you haven’t linked in the CoreData framework. Make sure that “CoreData.framework” is part of the “Link binary with libraries” phase of the target you’re building. Also add #import <CoreData/CoreData.h> in .h file.