how to fix xcdatamodel error at linker xcode?
===

  I make a new xcdatamodeld with 2 entity

1. stage, this one have a relationship many to level

2. level, this one have many attribute and a relationship one with stage

  [2]: http://i.stack.imgur.com/pC1rH.png

but when I create NSManagedObject subclass from that xcdatamodeld, and build my project.. there are 3 error log

like this:


    Undefined symbols for architecture i386:
          "_OBJC_METACLASS_$_NSManagedObject", referenced from:
              _OBJC_METACLASS_$_Stage in Stage.o
              _OBJC_METACLASS_$_Level in Level.o
          "_OBJC_CLASS_$_NSManagedObject", referenced from:
              _OBJC_CLASS_$_Stage in Stage.o
              _OBJC_CLASS_$_Level in Level.o
        ld: symbol(s) not found for architecture i386
        clang: error: linker command failed with exit code 1 (use -v to see invocation)


  [1]: http://i.stack.imgur.com/F3uGv.png


anyone have this trouble too?

How can I fix that error?

I am newbie at xcode and IOS programmer, thank you in advance ^^
