Query database in django using model procedure

Question

I have created model with procedure that subtract two dates from fields in model returning days difference between them, for example:

class Example:
    earlierDate=models.DateField()
    laterDate=models.DateField()

    def day_diff(self):
        return (laterDate-earlierDate).days

Is it possible to query database including day_diff procedure ?

in_views_query=Example.objects.filter(day_diff__gte=30)

When i use this kind o query it shows me that there is no field 'day_diff'

Regards

check this out, let me know if that helps: stackoverflow.com/q/805393/9102309 — Vedprakash Upraity
– Vedprakash Upraity, Commented Jun 19, 2020 at 11:39

minglyu · Accepted Answer · 2020-06-19 13:56:59Z

2

You can use ExpressionWrapper to make this happen

from django.db.models import DateField, ExpressionWrapper, F

Example.objects.annotate(day_diff=ExpressionWrapper(
                F('laterDate') - F('earlierDate'), output_field=models.DateField()
))

Django also has a similar example in docs. check it out: https://docs.djangoproject.com/en/3.0/ref/models/expressions/#using-f-with-annotations

answered Jun 19, 2020 at 13:56

minglyu

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