XCode 4.2 NSManagedObject context build failed <p>I created an UserModel.xcdatamodeld with one Entry: UserBase, and I added an attribute which name is UserID and type is Integer 32.</p> <p>After that, I create classes for it with file->new file->NSManagedOBject subclass, which creates UserBase.h and .m automatically.</p> <p>In my controller imported the UserBase.h file, and create a property:</p> <pre><code>NSManagedObjectContext *userBaseObjectContext; </code></pre> <p>with</p> <pre><code>@property (nonatomic, retain) NSManagedObjectContext *userBaseObjectContext; </code></pre> <p>In mycontroller.m file synthetized the userBaseObjectContext property and in DidLoad function I tried this:</p> <pre><code>UserBase *userObject=(UserBase *)[NSEntityDescription insertNewObjectForEntityForName:@"UserBase" inManagedObjectContext:userBaseObjectContext]; [userObject setUserID:[NSNumber numberWithInt:42]]; NSError *error; if(![userBaseObjectContext save:&amp;error]) { UIAlertView *alert=[[UIAlertView alloc]initWithTitle:@"Application error" message:@"error" delegate:nil cancelButtonTitle:@"Close" otherButtonTitles:nil,nil]; [alert show]; [alert release]; } else NSLog(@"not working..."); </code></pre> <p>When I try to build my project, I got this error:</p> <pre><code>Undefined symbols for architecture i386: "_OBJC_CLASS_$_NSEntityDescription", referenced from: objc-class-ref in LoginController.o "_OBJC_METACLASS_$_NSManagedObject", referenced from: _OBJC_METACLASS_$_UserBase in UserBase.o "_OBJC_CLASS_$_NSManagedObject", referenced from: _OBJC_CLASS_$_UserBase in UserBase.o ld: symbol(s) not found for architecture i386 clang: error: linker command failed with exit code 1 (use -v to see invocation) </code></pre> <p>What is that means?</p> <p>I followed this tutorial: <a href="http://mobile.tutsplus.com/tutorials/iphone/iphone-core-data/">http://mobile.tutsplus.com/tutorials/iphone/iphone-core-data/</a></p>