How to Group and Sum Category with ORM-Query - django

Question

Please note: Similar questions didn't help me as they have the category-foreignkey in the same class.
I have a simple Invoice app with models Invoice, Position, Product and Category. The Product is bound to the Category.
My target is to create a queryset that
filters e. g. a specific date-range
and then group all categories and build their sums
Here is a screenshot of the invoice respectively of its positions:
The expected result of the grouped query should look like this:
Can you help me to create a query that groups and sums the categories within the filtered date-range?
The only solution I was able to create was the filter of a specific date-range:
queryset = Position.objects.filter(invoice__date_of_purchase__range=['2019-01-01', '2019-12-31'])
models.py (which I have simplified):
from django.db import models
from django.urls import reverse
class Category(models.Model):
name = models.CharField(max_length=30, unique=True)
def __str__(self):
return self.name
class Product(models.Model):
name = models.CharField(max_length=120)
category = models.ForeignKey(Category, on_delete=models.CASCADE, related_name='products')
def __str__(self):
return self.name
class Invoice(models.Model):
invoice_code = models.CharField(max_length=15)
date_of_purchase = models.DateField()
customer_name = models.CharField(max_length=100)
def __str__(self):
return self.invoice_code
class Position(models.Model):
invoice = models.ForeignKey(Invoice, on_delete=models.CASCADE)
product = models.ForeignKey(Product, on_delete=models.CASCADE)
quantity = models.DecimalField(decimal_places=2, max_digits=6)
price = models.DecimalField(decimal_places=2, max_digits=8)
total = models.DecimalField(
decimal_places=2, max_digits=8, blank=True, null=True) # is calculated in view
def __str__(self):
return self.product.name

Answer 1

The following filter will return all categories that have an invoice in the date range and will also filter the annotation to sum only those positions for those invoices
categories = Category.objects.filter(
products__position__invoice__date_of_purchase__range=['2019-11-17', '2019-12-31']
).annotate(
sum=Sum('products__position__total')
)
Each category will now be annotated with an attribute "sum"
for category in categories:
print(category, category.sum)

Answer 2

I'm going to suggest a tweak based on my experience.
Put position into the invoice model as a many to many fields. This should make it cheaper to filter the date range of invoices. It also may help to add a "sent" bol field depending on your use case.
Either in your view or in a utils.py file. Loop thru the query set's "Position's" field with the category as the conditional to separate by category and += the Position.total field to your awaiting variable.