Django - FileField upload_to with filename from other field's primary key -

i have django model:

class observationmedia(models.model):     observation = models.foreignkey(observation)       audio_file = audiofilefield   ( upload_to=audio_dir, blank=true, null=true )     photo_file = models.imagefield( upload_to=img_dir,   blank=true, null=true ) 

where table media linked table (observation) media related to.

how can save audiofilefield (just superclass of filefield) , imagefield name of files primary key of observation, e.g. 2465.jpg? i'm allowed pass 'instance' , 'filename' upload_to, far know, don't know how pass parameter.

you can pk instance. this:

def get_audio_path(instance, filename):    return os.path.join(audio_dir+instance.observation.pk+".jpg")  class observationmedia(models.model):    observation = models.foreignkey(observation)      audio_file = audiofilefield   ( upload_to=get_audio_path, blank=true, null=true )