CODEWITHSUNDEEP
pythondjango
Nitin Raturi
Nitin Raturi

Reputation: 1835

How to update exisiting date field in django using existing days field?

I want to update existing date field in django using existing days field in the same table.

For example

class Sample(models.Model):
    notify_status = models.BooleanField(default=0)
    next_date = models.DateField(blank=True, null=True)
    days = models.IntegerField(blank=True, null=True)

Now I want to add days to next_date where next_date is less than todays date.

I have tried this:

import datetime
from django.db.models import F

Sample.objects.filter(next_date__lt=today).update(next_date=F('next_date')+datetime.timedelta(days=F('days')))

But its not working. Here is the output

Something went wrong in period_retrack.py: unsupported type for timedelta days component: F

Expected Output I want next_date to be increased by the number of days in the same table for every row where next_date is less than current_date i.e, today's date

Upvotes: 1

Views: 1106

Answers (1)

Michel Sabchuk
Michel Sabchuk

Reputation: 840

You can cast the days field value to an interval at the database level:

import datetime

from django.db.models import CharField, DurationField, F, Value
from django.db.models.functions import Cast, Concat

Sample.objects.filter(next_date__lt=today).update(
    next_date=F("next_date")
    + Cast(
        Concat("days", Value(" days"), output_field=CharField()),
        output_field=DurationField(),
    )
)

Notice that I'm doing the cast in 2 steps:

  1. Concatenate the value with the " days" suffix (e.g. "1 days")
  2. Cast this string to a duration

This would work with Postgres, I'm not sure about other databases.

Upvotes: 1

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