Change Field of Foreign Key Object

I have the following problem.

I have a model Towar :

class Towar(models.Model):
  nrSeryjny = models.CharField(max_length=100)
  opis = models.CharField(max_length=255)
  naStanie = models.NullBooleanField(null=True)

  def __unicode__(self):
      return "%s" % self.opis

  def lowerName(self):
      return self.__class__.__name__.lower()

  def checkState(self):
      return self.naStanie

  def changeState(self,state):
      self.naStanie=state

  class Meta:
      ordering=['nrSeryjny']
      app_label = 'baza'
      permissions=(("view_towar","mozna miec podglad dla towar"),)

and another model, Wypozyczenie , which is linked to Towar by a foreign key relationship:

class Wypozyczenie(models.Model):
    dataPobrania = models.DateField()
    pracownik = models.ForeignKey(User,null=True)
    kontrahent = models.ForeignKey(Kontrahenci,null=True)
    towar = models.ForeignKey(Towar,null=True)
    objects = WypozyczenieManager()
    default_objects = models.Manager()

    ZwrotyObjects = WypozyczenieZwrotyManager()

    def lowerName(self):
        return self.__class__.__name__.lower()

    def __unicode__(self):
        if self.towar == None:
            return "Dla:%s -- Kto:%s -- Kiedy:%s -- Co:%s" % (self.kontrahent,self.pracownik,self.dataPobrania,"Brak")
        else:
            return "Dla:%s -- Kto:%s -- Kiedy:%s -- Co:%s" % (self.kontrahent,self.pracownik,self.dataPobrania,self.towar)

    class Meta:
        ordering = ['dataPobrania']
        app_label = 'baza'
        permissions = (("view_wypozyczenie","mozna miec podglad dla wypozyczenie"),)

and a view to add models:

def modelAdd(request,model,modelForm):
    mod = model()
    if request.user.has_perm('baza.add_%s' % mod.lowerName()):
        if request.method == 'POST':
            form=modelForm(request.POST)
            if form.is_valid():
                form.save()
                return HttpResponseRedirect('/'+ mod.lowerName() + '/')
        else:
            form = modelForm()
            v = RequestContext(request,{'form':form})
            return render_to_response('add_form.html',v)

What I want is that when I add Wypozyczenie and save it, then the Towar that is stored by Wypozyczenie changes its naStanie field from True to False.

Greets

---

If you want to always keep those two in sync you can override Wypozyczenie's save() method.

class Wypozyczenie(models.Model):
    ...

    def save(self):
        self.towar.naStanie = False
        self.towar.save()

Alternatively, you can also override ModelForm's save() method.

---

What have you tried?

Can't you just put

myinstance = form.save()
towar = myinstance.towar
towar.naStanie = False
toware.save()

instead of your simple call to form.save() in your view.

---

You can use signals emitted when saving your Wypozyczenie object. It might be a little "cleaner" than overriding save() , especially when it's useful to re-use the function for other models:

@receiver(models.signals.post_save, sender=Wypozyczenie)
def after_wypozyczenie_save(sender, instance, created, **kwargs):
    # `instance` is your saved Wypozyczenie object, you can
    # access all it's fields here:
    instance.towar.naStanie = False
    instance.towar.save()

    # It's also possible to do different action on the first save
    # and on subsequent updates:
    #
    # if created:
    #     ...
    # else:
    #     ...

There are other signals sent before saving or on deletion. Django documentation on signals is quite helpful here.

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