How to perform an F() query with datetime field?

Question

I want to do a query based on two fields of a model, a date, offset by an int, used as a timedelta

model.objects.filter(last_date__gte=datetime.now()-timedelta(days=F('interval')))

My model goes this way:

class Line(models.Model):
    last_date = models.DateTimeField(auto_now=True)
    interval = models.IntegerField(default=0)

I am using Django 2.0 and db.sqlite3

I found some sources What is the replacement for DateModifierNode in new versions of Django and Making queries using F() and timedelta at django but they were not helpful.

some suggested to use duration field, but I want the interval to be entered in days desperately, whenever I use duration field , the admin needs to enter that in [days hh:mm:ss] in admin forms.

And some gave a method

model.objects.filter(last_date__gte=datetime.now()-timedelta(days=1)*F('interval'))

which isn't working in db.sqlite3 and returning errors.

Please suggest me some solution,like admin using duration field and entering only days or some solution with integer field of days.

What type is `interval`? Please post the relevant parts of your model. — Willem Van Onsem, Jul 08 '18 at 20:33
@SiddanathamSaikalyan Maybe it would be best to use a `DurationField` for the `interval` and then register a custom [form](https://docs.djangoproject.com/en/2.0/topics/forms/) for the admin view, which allows entering just the number of days. — a_guest, Jul 08 '18 at 20:53

score 0 · Accepted Answer · answered Jul 09 '18 at 07:39

I handled the situation this way:

class Line(models.Model):
  last_date = models.DateTimeField(auto_now=True)
  interval1 = models.IntegerField(default=0)
  interval2 = models.DurationField(default=0)

  def save(self, *args, **kwargs):
    self.interval2 = timedelta(days=self.interval1)
    super(Line, self).save(*args, **kwargs)

I used two fields, and while saving I converted interval1(integer field) to interval2(DurationField) and excluded interval2 in the forms, then Filter can be applied easily.

  model.objects.filter(last_date__gte=datetime.now()- F('interval2'))

How to perform an F() query with datetime field?

1 Answers1