python - Django admin double filter reverse foreign key lookup -

i'm trying reverse in admin form 2 different fields, 1 parent of each other. idea i've got following hierarchy of dropdown menus.

area

linea (filtered area) fk = area

sensor (filtered linea) fk = linea.

add sensor details.

right i'm trying modifying modelform adding sensors adding self reffering filters foreign keys , making modeladmin. so:

class sensorform(forms.modelform):     def __init__(self, *args, **kwargs):         super(sensorasignado, self).__init__(*args, **kwargs)         self.fields['linea'].queryset = linea.objects.filter(no_de_linea = self.instance.linea)         self.fields['area'].queryset = area.objects.filter(linea.objects.filter(no_de_linea = self.instance.linea))  class sensoradmin(admin.modeladmin):     form = sensorform 

the idea have 2 fields, linea , area, linea filtered area, , sensor filtered linea.

here's snippet of models:

class area(models.model):     area_nom = models.charfield(max_length = 20)     description = models.textfield()      def __str__(self):         return self.area_nom  # rack del cual fue sacada la pieza     class linea(models.model):     linea_nom = models.charfield(max_length = 20)     area = models.foreignkey('area')     description = models.textfield()      def __str__(self):         return self.linea_nom  # sensor del cual se sacó la lectura class sensorasignado(models.model):     sensor_nom = models.charfield(max_length = 20)     linea = models.foreignkey('linea')     sensor_tipo = models.foreignkey('tipodesensor')      def __str__(self):         return self.sensor_nom 

thanks lot in advance , hope have day.