[Django]-How can I get a total count of a model's related objects and the model's children's related objects?

3👍

✅

I think the most efficient way of calculating this is at write time. You should modify OrganizationalUnit like this:

class OrganizationalUnit(models.Model):
    name = models.CharField(max_length=100)
    parent = models.ForeignKey(
        'self',
        blank=True, null=True,
        related_name='children',
    )
    checkout_number = models.IntegerField(default=0)

create the functions that will update the OrganizationalUnit and its parents at write time:

def pre_save_checkout(sender, instance, **kwargs):
    if isinstance(instance,Checkout) and instance.id and instance.department:
         substract_checkout(instance.department)

def post_save_checkout(sender, instance, **kwargs):
    if isinstance(instance,Checkout) and instance.department:
         add_checkout(instance.department)

def  substract_checkout(organizational_unit):
    organizational_unit.checkout_number-=1
    organizational_unit.save()
    if organizational_unit.parent:
        substract_checkout(organizational_unit.parent)

def  add_checkout(organizational_unit):
    organizational_unit.checkout_number+=1
    organizational_unit.save()
    if organizational_unit.parent:
        add_checkout(organizational_unit.parent)

now all you need is connect those functions to the pre_save, post_save and pre_delete signals:

from django.db.models.signals import post_save, pre_save, pre_delete

pre_save.connect(pre_save_checkout, Checkout)
pre_delete.connect(pre_save_checkout, Checkout)
post_save.connect(post_save_checkout, Checkout)

That should do it…

👤Julian

[Django]-Validating data in Django ModelForm

3👍

What you need is a recursive function that traverse OrganizationalUnit relation tree and gets number of related Checkouts for each OrganizationalUnit. So your code will look like this:

def count_checkouts(ou):
   checkout_count = ou.checkouts.count()
   for kid in ou.children.all():
       checkout_count += count_checkouts(kid)
   return checkout_count

Also note, that to get a number of related checkouts I use: