On Thu, Feb 7, 2013 at 1:54 PM, vijay shanker <[email protected]> wrote: > Hi > I am using django version 1.4.3 > I am using two signals in my models.py > one is m2m_changed, so i can have a counter field (numcounter) of number of > m2m fields attached, and another is post_save so i can decide whether to > have a OneToOneField (cartrule, is to be applied only if there are more than > 2 fields) or not. > my models.py is: > > class CartItem(models.Model): > content_type = models.ForeignKey(ContentType) > object_id = models.PositiveIntegerField() > content_object = generic.GenericForeignKey(' > content_type','object_id') > quantity = models.PositiveIntegerField(default=0) > is_abandoned = models.BooleanField(default=False) > created_at = models.DateTimeField(auto_now_add=True) > update_at = models.DateTimeField(auto_now=True) > def __str__(self): > return self.content_object.name > > class CartRule(models.Model): > ##some field > pass > > class Cart(models.Model): > cart_id = models.CharField(max_length=50, null=False) > customer = models.ForeignKey(Customer,null=True,blank=True) > cartitems = models.ManyToManyField(CartItem,null=True) > created_at = models.DateTimeField(auto_now_add=True) > update_at = models.DateTimeField(auto_now=True) > cartrule = > models.OneToOneField(crapclass,null=True,blank=True) > num_cartitem = models.IntegerField() > def __str__(self): > return self.cart_id > > @receiver(post_save, sender=Cart) > def apply_condition(sender,instance,created,raw,using,*args,**kwargs): > # i want to decide here if num_cartitem is greater than 2 its ok to have > a cartrule > pass > > @receiver(m2m_changed) > def save_cartitem_counter(sender, instance, signal,*args, **kwargs): > if kwargs['action'] == 'post_add': > instance.num_cartitem = instance.cartitems.all().count() > instance.save() > > the issue is apply_condition gets called twice, with similar value of args, > first with older value of m2m (cartitem) field in Cart, the other time with > the values i intended to save > I looked into older post but still could not figure out the whys.How should > i go about this ? >
When you save a Cart instance, the post_save signal is triggered. If the M2M relationship is changed as well, then the m2m_changed signal is triggered. Your handler for this then re-saves the Cart instance after denormalising data, which triggers the post save signal for a second time. You should probably connect the M2M receiver to a specific sender too, currently it will fire whenever any M2M on any model is changed. Keeping denormalized data like that is a pain, could you do without it, and re-calculate it where necessary? Alternatively, you could use a named intermediary M2M relationship: https://docs.djangoproject.com/en/1.4/topics/db/models/#intermediary-manytomany and connect signals on post_create and post_delete to the intermediary model, updating the Cart as necessary. This is a little more logical, since you wish to denormalise the data whenever an item is added to or removed from a cart, ie whenever a row is added or deleted to the intermediate table. Naming the relationship allows you to connect the signals to the right place. Cheers Tom -- You received this message because you are subscribed to the Google Groups "Django users" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at http://groups.google.com/group/django-users?hl=en. For more options, visit https://groups.google.com/groups/opt_out.
