further, i tried putting a sender argument in receiver, but the sender , i found (by set_trace) is Cart_cartitems, how can i import this <class 'shoppingcart.models.Cart_cartitems'> when its only a intermediary model that django's creating. On Friday, February 8, 2013 11:26:47 AM UTC+5:30, vijay shanker wrote: > > Thanks Evans.That was helpful. :) > > On Thursday, February 7, 2013 7:54:36 PM UTC+5:30, Tom Evans wrote: >> >> 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 >> >
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