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

I did it this way

.annotate(date_str=ExpressionWrapper(
            Func(F('date'), Value('%d/%m/%Y %H:%i'), function='DATE_FORMAT'), output_field=CharField()
        ))

Answer 2

https://docs.djangoproject.com/en/2.2/ref/models/fields/#datetimefield

A date and time, represented in Python by a datetime.datetime instance.

You can get a string representation of a DateTimeField casting it directly:

str(obj)
# obj = qs[0][0] ? or qs[0][1] ?

You'll get result like this (in this example I use datetime.datetime.now() since a DateTimeField is represented by datetime.datetime is the same behavior):

>>> now = datetime.datetime.now()
>>> str(now)
'2013-06-26 00:14:26.260524'

if you want less information or formatted in other mode you can use strftime() function for format them. see:

>>> now.strftime('%Y-%m-%d %H:%M')
'2013-06-26 00:14'

Answer 3

If you are using Postgres, you can do it like this (date format options here). The solution is database dependent, but it sure beats looping though a long list in Python land after your perform the query.

qs = MyModel.objects.filter(name='me')
qs = qs.extra(select={'datestr':"to_char(activation_date, 'YYYY-MM-DD HH24:MI:SS')"})
qs = qs.values_list('datestr')

I am sure MySQL has some equivalent function as Postgres's to_char, but you'll have to find that on your own as I am not a MySQL guy.

Answer 4

qs = MyModel.objects.filter(name='me')
qs = qs.extra(select={'datestr':"DATE_FORMAT(activation_date, '%Y-%m-%d')"})
qs = qs.values_list('datestr')

Answer 5

You can also convert the date in queryset to string using map function. Example:

qs = MyModel.objects.filter(name='me').values_list('activation_date', flat=True)
data = map(str, qs)

Answer 6

extra() is an old API that Django aims to deprecate at some point in the future. I would avoid using it.

Try the following instead:

from django.db.models import F, Func, Value, CharField

qs.annotate(
  formatted_date=Func(
    F('date'),
    Value('dd.MM.yyyy hh:mm'),
    function='to_char',
    output_field=CharField()
  )
)

This works only with a database that supports the to_char date type formatting function. Postgres provides this function by default. If you use a MSSQL backend you could swap to_char with FORMAT. For Oracle consult their documentation, etc.

After the queryset is evaluated this will add the annotation formatted_date to each object in the queryset that is returned.