Unable to combine with Extract function

[sevdog]

When using this field is not possible to direcly use the Django ORM function Extract (and similars).

Since this function checks field type before passing to database:

ValueError: Extract input expression must be DateField, DateTimeField, TimeField, or DurationField.

This does not allow the developer to use with ease the postgres DB function EXTRACT.

[sevdog]

A workaround for this is to use ExpressionWrapper:

from django.db.models import  DurationField, ExpressionWrapper, F 
from django.db.models.functions import Extract

MyModel.objects.annotate(
  epoch=Extract(
    ExpressionWrapper(F('myfield'), DurationField()),
    'epoch',
  ),
)