Re: post_save signal getting called twice !

[vijay shanker]

yes that was it. thanks a ton. ;)

On Friday, February 8, 2013 5:21:19 PM UTC+5:30, Martin J. Laubach wrote:
>
> 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 > 'shoppingcart.models.Cart_cartitems'> when its only a intermediary model 
>> that django's creating.
>
>
>   I think you want Cart.cartitems.through
>
>   mjl
>
>

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Re: post_save signal getting called twice !

[Martin J. Laubach]

>
> 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  'shoppingcart.models.Cart_cartitems'> when its only a intermediary model 
> that django's creating.


  I think you want Cart.cartitems.through

  mjl

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Re: post_save signal getting called twice !

[vijay shanker]

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  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  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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Re: post_save signal getting called twice !

[vijay shanker]

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 
>  
> 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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Re: post_save signal getting called twice !

[Tom Evans]

On Thu, Feb 7, 2013 at 1:54 PM, vijay shanker  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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post_save signal getting called twice !

[vijay shanker]

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 ?

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