How to use sql statement in django?

I want to get the latest date from my database. Here is my sql statement.

select "RegDate"
from "Dev"
where "RegDate" = (
 select max("RegDate") from "Dev")

It works in my database. But how can I use it in django?

I tried these codes but it return error. These code are in views.py.

Version 1:

lastest_date = Dev.objects.filter(reg_date=max(reg_date)) 

Error:

'NoneType' object is not iterable

Version 2:

last_activation_date = Dev.objects.filter(regdate='reg_date').order_by('-regdate')[0]

Error:

"'reg_date' value has an invalid format. It must be in YYYY-MM-DD HH:MM[:ss[.uuuuuu]][TZ] format."

I’ve defined reg_date at beginning of the class.

What should I do for this?

Answer

You make things too complicated, you simply order by regdate, that’s all:

last_activation_dev = Dev.objects.order_by('-regdate').first()

The .first() will return such Dev object if it is available, or None if there are no Dev objects.

If you only are interested in the regdate column itself, you can use .values_list(..):

last_activation_date = Dev.objects.order_by('-regdate').values_list('regdate', flat=True).first()

By using .filter() you actually were filtering the Dev table by Dev records such that the regdate column had as value 'reg_date', since 'reg_date' is not a valid datetime format, this thus produced an error.