conversion of datetime Field to string in django queryset.values_list()

Question

I have a queryset like:

qs = MyModel.objects.filter(name=\'me\').values_list(\'activation_date\')

here activation_date is

Answer 1

extra is deprecated in Django 2.0

That's why I think the best solution to get a stringified datetime is:

foo_bar = FooBarModel.objects.annotate(
    str_datetime=Cast(
        TruncSecond('some_datetime_field', DateTimeField()), CharField()
    )
).values('str_datetime').first()

The result is:

foo_bar.str_datetime:
(str)'2014-03-28 15:36:55'

---

Also I'd like to mention that you can format it as well in any way you want like:

from django.db.models import Value

foo_bar = FooBarModel.objects.annotate(
    day=Cast(ExtractDay('some_datetime_field'), CharField()),
    hour=Cast(ExtractHour('some_datetime_field'), CharField()),
    str_datetime=Concat(
        Value('Days: '), 'day', Value(' Hours: '), 'hour', 
        output_field=CharField()
    )
).values('str_datetime').first()

The result is:

foo_bar.str_datetime:
(str)'Days: 28 Hours: 15'

Answer 2

Very surprised to see that no one suggested the cast to a simple TextField (note, I'm using Postgres so I can't confirm for other RDBMSes):

queryset = FooBarModel.objects.values(my_datetime=Cast('some_datetime_field', TextField()))
foo_bar = queryset.first()
foo_bar['my_datetime']
>>> u'2019-10-03 17:59:37.979578+00'

It similarly also works fine for nested fields:

queryset = FooBarModel.objects.values(Cast('baz__some_datetime_field', TextField()))

Alternatively, a custom Func can also be used (also specific to Postgres here, but can be modified for any other RDBMS):

class FullDateTimeCast(Func):
   """
   Coerce an expression to a new field type.
   """
   function = 'TO_CHAR'
   template = '%(function)s(%(expressions)s, \'FMDay, Month DD, YYYY at HH12:MI:SS AM\')'

queryset = FooBarModel.objects.values(my_datetime=FullDateTimeCast('some_datetime_field', TextField()))
foo_bar = queryset.first()
foo_bar['my_datetime']
>>> u' Thursday, October 03, 2019 at 17:59:37 PM'