CODEWITHSUNDEEP
pythondjangodjango-modelsdjango-orm
Rahul Singh
Rahul Singh

Reputation: 27

Django - Filter based on nested sum of related values

I have 3 Django models like this

Request is a donation request, RequestItem denotes how many instances of the name item are needed, Donation denotes how many donations have been done for the connected item

class Request:
    pass


class RequestItem:
    name
    request = ForeignKey(Request)
    needed = IntegerField()


class Donation:
    item = ForeignKey(RequestItem)
    donated = IntegerField()

A RequestItem a is said to be complete if

a.needed == Sum(donation.donated for each donation in a.donation_set.all()

A Request r is said to be complete if

For every RequestItem ri in r.request_item_set.all(); ri is complete

I need to filter out the requests which are complete/aren't complete.

Upvotes: 0

Views: 113

Answers (1)

Timofey Chernousov
Timofey Chernousov

Reputation: 1294

If you are sure sum of 'donated' will never exceed value of 'needed' for every request item, you could do this way:

from django.db.models import Sum, F
Request.objects.annotate(needed=Sum('requestitem__needed', distinct=True), donated=Sum('requestitem__donation__donated')).filter(donated__gte=F('needed'))

Here sum of all donations per request is compared against sum of all 'needed' values for the same request. If former is greater or equivalent, request could be considered as completed

Upvotes: 1

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