All of these functions are available from the django.contrib.postgres.functions module.
Returns the date and time on the database server that the current transaction started. If you are not in a transaction it will return the date and time of the current statement. This is a complement to django.db.models.functions.Now, which returns the date and time of the current statement.
Note that only the outermost call to atomic() sets up a transaction and thus sets the time that TransactionNow() will return; nested calls create savepoints which do not affect the transaction time.
Usage example:
>>> from django.contrib.postgres.functions import TransactionNow
>>> Article.objects.filter(published__lte=TransactionNow())
[<Article: How to Django>]
Mar 31, 2016