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 <deon...@gmail.com> 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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