Change Field of Foreign Key Object - django

Question

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

Answer 1

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.

Answer 2

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.

Answer 3

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.