Floor Division and Modulo in ListView Django - django

Question

With Django Listview, is it possible to display new columns that contain the values of floor division and modulo?
I have the following two models:
models.py
class Model_Item(models.Model):
item_name = models.CharField(max_length = 100, null = False, blank = False, unique = True)
item_bottleperpack = models.FloatField(null = True, blank = False) # e.g. 100 bottles per pack
def __unicode__(self):
return self.item_name
class Model_ItemTransaction(models.Model):
item = models.ForeignKey(Model_Item, to_field = "item_name")
item_sold = models.FloatField(null = True, blank = True) # in terms of bottle
def __unicode__(self):
return self.item
With this listview:
views.py
class View_Item(ListView):
def get_queryset(self):
queryset = Model_Item.objects.all()
queryset = queryset.annotate(
sum_ = Sum("model_itemtransaction__item_sold")
)
queryset = queryset.annotate(
floor_division_ = F("sum_") // F("item_bottleperpack"),
module_ = F("sum_") %% F("item_bottleperpack")
)
return queryset
Basically, if I have sold, say 650 bottles, and there is 100 bottles per pack, I would like the listview to display:
6 packs on the "floor-division" column, and
50 bottles on the "modulo" column.
Currently I am receiving the following errors with my current code
unsupported operand type(s) for //: 'F' and 'F'
and
unsupported operand type(s) for %%: 'F' and 'F'
and hoping someone could help me find any solution to this (and it does not have to be with conditional expression).

Answer 1

According to https://docs.djangoproject.com/en/2.0/_modules/django/db/models/expressions/:
Neither class F nor it's parent Combinable implement __floordiv__, so // is not implemented. Combinable does implement __truediv__, which is the / operator.
I haven't heard of the operator %% in Python, but % will work because __mod__ is implemented in Combinable.
Try using models.IntegerField or models.PositiveIntegerField for item_bottleperpack and item_sold, and updating this line in views.py:
queryset = queryset.annotate(
floor_division_ = F("sum_") / F("item_bottleperpack"),
module_ = F("sum_") % F("item_bottleperpack")
)
I'm assuming that Combinable will return an integer as the output of dividing two integers -- this might not be the case. If so, you might want to round down the result.

Answer 2

So I have found a way to solve this, thanks to this post.
First I cleaned the code at views.py,
views.py
class View_Item(ListView):
def get_queryset(self):
queryset = Model_Item.objects.all()
queryset = queryset.annotate(
sum_ = Sum("model_itemtransaction__item_sold")
)
return queryset
then added this code file into the templatetags folder,
app_filters.py
from django import template
register = template.Library()
#register.filter(name = "func_floor_division")
def func_floor_division(num, val):
if num:
floor_division = num // val
return floor_division
else:
return None
#register.filter(name = "func_modulo")
def func_modulo(num, val):
if num:
modulo = num % val
return modulo
else:
return None
and finally modified the tags in the html file.
html
{% load app_filters %}
<table>
<tr>
<th>Floor Division</th>
<th>Modulo</th>
</tr>
{% for obj_ in object_list %}
<tr>
<td>{{ obj_.sum_|func_floor_division:obj_.item_bottleperpack }}</td>
<td>{{ obj_.sum_|func_modulo:obj_.item_bottleperpack }}</td>
</tr>
{% endfor %}
</table>
Hope this helps for anyone who is encountering the same issue.

Answer 3

you can create a new floor_division and module_ fields in your Model_Item, then you use the post save receiver to update the floor_division and module_ fields
from django.db.models.signals import pre_save
class Model_Item(models.Model):
item_name = models.CharField(max_length = 100, null = False, blank = False, unique = True)
item_bottleperpack = models.FloatField(null = True, blank = False) # e.g. 100 bottles per pack
floor_division = models.IntegerField(null=True, blank=True)
module_ = models.IntegerField(null=True, blank=True)
def __unicode__(self):
return self.item_name
def model_item_pre_save(sender, instance, created):
item = Model_Item.objects.get(id=instance.id)
item_transaction = Model_Transaction.objects.get(item_id=instance.id)
item.floor_division = item_transaction.item_sold // item.item_bottleperpack
item.module_ = item_transaction.item_sold %% item.item_bottleperpack
pre_save.connect(model_item_pre_save, sender=Model_Item)