Hi, I'm trying to apply a predicate to a core data fetch and hitting EXC_BAD_ACCESS.

I've successfully used NSPredicate to filter an array's contents, but all my attempts to use NSPredicate with Coredata fail. 

I'm using framework 'Coredata' and framework 'Foundation' and this is the method that fails:

  def tagEntityExists?(tag, moc)

    puts 'NodeProxy:tagEntityExists?'

    entityDescription = NSEntityDescription.entityForName('Tag', inManagedObjectContext:moc)

    request = NSFetchRequest.alloc.init()

    request.setEntity(entityDescription)

    

    puts "Looking for tag: #{tag}"

    predicate = NSPredicate.predicateWithFormat("name == %@", tag)

    request.setPredicate(predicate)

    

    error = Pointer.new(:id)

    

    puts "request: #{request.description}"

    begin

      results = moc.executeFetchRequest(request, error:error)

    rescue Exception => bang

      puts bang

    end

    

    unless results

      puts "Fetch failure: #{error.description}"

      return nil

    end

    puts "Will return: #{results.inspect}"

    return results[0]

  end

and here's the backtrace I get:

#0  0x00007fff86ef42bc in _qfqp2_InitializedGlobalData ()

#1  0x0000000102d61fe0 in ?? ()

#2  0x000000010014a0b3 in rb_vm_dispatch ()

#3  0x0000000102d5ab26 in ?? ()

#4  0x0000000102d62c56 in ?? ()

#5  0x000000010014bcd6 in rb_vm_dispatch ()

#6  0x0000000102d5ab26 in ?? ()

#7  0x0000000102d626da in ?? ()

#8  0x000000010014e1f7 in rb_vm_yield_args ()

#9  0x0000000100102ad8 in rb_yield ()

#10 0x0000000100176f38 in rb_ary_freeze ()

#11 0x000000010014bd16 in rb_vm_dispatch ()

#12 0x0000000102d5ab26 in ?? ()

#13 0x0000000102d62383 in ?? ()

#14 0x000000010014bcd6 in rb_vm_dispatch ()

#15 0x0000000102d5ab26 in ?? ()

#16 0x0000000102d61906 in ?? ()

#17 0x000000010014bcfb in rb_vm_dispatch ()

#18 0x0000000102d5ab26 in ?? ()

#19 0x0000000102d61542 in ?? ()

#20 0x000000010014e1f7 in rb_vm_yield_args ()

#21 0x0000000100102ad8 in rb_yield ()

#22 0x0000000100176f38 in rb_ary_freeze ()

#23 0x000000010014bd16 in rb_vm_dispatch ()

#24 0x0000000102d5ab26 in ?? ()

#25 0x0000000102d60c59 in ?? ()

#26 0x000000010014bd16 in rb_vm_dispatch ()

#27 0x0000000102d5ab26 in ?? ()

#28 0x0000000102d6073d in ?? ()

#29 0x000000010014bcfb in rb_vm_dispatch ()

#30 0x00000001000f2bbe in rb_objc_isEqual ()

#31 0x00000001000f2d8e in rb_objc_isEqual ()

#32 0x00007fff837d1e9a in -[NSApplication sendAction:to:from:] ()

#33 0x00007fff837f641e in -[NSMenuItem _corePerformAction] ()

#34 0x00007fff837f6188 in -[NSCarbonMenuImpl performActionWithHighlightingForItemAtIndex:] ()

#35 0x00007fff83a7a279 in -[NSMenu _internalPerformActionForItemAtIndex:] ()

#36 0x00007fff8392bf77 in -[NSCarbonMenuImpl _carbonCommandProcessEvent:handlerCallRef:] ()

#37 0x00007fff837d895c in NSSLMMenuEventHandler ()

#38 0x00007fff8109b9d5 in DispatchEventToHandlers ()

#39 0x00007fff8109af28 in SendEventToEventTargetInternal ()

#40 0x00007fff810b8beb in SendEventToEventTarget ()

#41 0x00007fff810e7d51 in SendHICommandEvent ()

#42 0x00007fff81114b86 in SendMenuCommandWithContextAndModifiers ()

#43 0x00007fff81114b3e in SendMenuItemSelectedEvent ()

#44 0x00007fff81114a3e in FinishMenuSelection ()

#45 0x00007fff810f5d13 in MenuSelectCore ()

#46 0x00007fff810f5468 in _HandleMenuSelection2 ()

#47 0x00007fff836a97dd in _NSHandleCarbonMenuEvent ()

#48 0x00007fff8367d317 in _DPSNextEvent ()

#49 0x00007fff8367c7a9 in -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] ()

#50 0x00007fff8364248b in -[NSApplication run] ()

#51 0x00007fff8363b1a8 in NSApplicationMain ()

#52 0x0000000102d5ea5d in ?? ()

#53 0x000000010014a658 in rb_vm_dispatch ()

#54 0x0000000102d5ab26 in ?? ()

#55 0x0000000102d5a4dc in ?? ()

#56 0x0000000100162d53 in rb_vm_run ()

#57 0x00000001000408f0 in ruby_run_node ()

#58 0x000000010015a332 in macruby_main ()

#59 0x0000000100000f20 in main (argc=1, argv=0x7fff5fbff6c8) at /Users/jonathan/Desktop/

Um, any suggestions? I see that there are previous list entries about this sort of problem but I think there are now all closed....

Many thanks and regards, Jonathan