Django ORM calculate number of days between two date attributes

Question

Scenario

I have a table student. it has following attributes

name,

age,

school_passout_date,

college_start_date

I need a report to know what is the avg number of days student get free between the passing the school and starting college.

Current approach

Currently i am irritating over the range of values finding days for each student and getting its avg.

Problem

That is highly inefficient when the record set gets bigger.

Question

Is there any ability in the Django ORM that gives me totals days between the two dates?

Possibility

I am looking for something like this.

Students.objects.filter(school_passed=True, started_college=True).annotate(total_days_between=Count('school_passout_date', 'college_start_date'), Avg_days=Avg('school_passout_date', 'college_start_date'))

Answer 1

You can do this like so:

Model.objects.annotate(age=Cast(ExtractDay(TruncDate(Now()) - TruncDate(F('created'))), IntegerField()))

This lets you work with the integer value, eg you could then do something like this:

from django.db.models import IntegerField, F
from django.db.models.functions import Cast, ExtractDay, TruncDate

qs = (
    Model
    .objects
    .annotate(age=Cast(ExtractDay(TruncDate(Now()) - TruncDate(F('created'))), IntegerField()))
    .annotate(age_bucket=Case(
        When(age__lt=30, then=Value('new')),
        When(age__lt=60, then=Value('current')),
        default=Value('aged'),
        output_field=CharField(),
    ))
)