I have the following two models.
class Product(models.Model):
product_group=models.ForeignKey('productgroup.ProductGroup', null=False,blank=False)
manufacturer=models.ForeignKey(Manufacturer, null=False,blank=False)
opening_stock=models.PositiveIntegerField(default=0)
class Meta:
unique_together = ('product_group', 'manufacturer')
and
TRANSACTION_TYPE=(('I','Stock In'),('O','Stock Out'))
class Stock(models.Model):
product=models.ForeignKey('product.Product', blank=False,null=False)
date=models.DateField(blank=False, null=False,)
quantity=models.PositiveIntegerField(blank=False, null=False)
ttype=models.CharField(max_length=1,verbose_name="Transaction type",choices=TRANSACTION_TYPE, blank=False)
I need to list all products with stock_in_sum=Sum(of all stock ins)
, stock_out_sum=Sum(of all stock outs)
and blance_stock=opening_stock+stock_in_sum - stock_out_sum
This is what I've achieved so far.
class ProductList(ListView):
model=Product
def get_queryset(self):
queryset = super(ProductList, self).get_queryset()
queryset = queryset.prefetch_related('product_group','product_group__category','manufacturer')
queryset = queryset.annotate(stock_in_sum = Sum('stock__quantity'))
queryset = queryset.annotate(stock_out_sum = Sum('stock__quantity'))
I need to get
stock_in_sum
as the sum(quantity) where ttype='I'
stock_out_sum
as the sum(quantity) where ttype='O'
blance_stock
as product.opening_stock + stock_in_sum - stock_out_sum
along with each Product object.
How do I achieve this?
Thanks.
You could use conditional aggregation
queryset = queryset.annotate(
stock_in_sum = Sum(Case(When(stock__ttype='I', then=F('stock__quantity')), output_field=DecimalField(), default=0)),
stock_out_sum = Sum(Case(When(stock__ttype='O', then=F('stock__quantity')), output_field=DecimalField(), default=0)))
)
To make the sums, and after that compute the balance with F() expression
queryset = queryset.annotate(balance_stock=F('opening_stock') + F('stock_in_sum') - F('stock_out_sum'))
You can also chain the different operation instead of multiple assignations:
queryset = queryset.prefetch_related(...).annotate(...).annotate(...)