using AS OF SYSTEM TIME

[luto]

Is there an any support for AS OF SYSTEM TIME in either the transaction variant:

BEGIN AS OF SYSTEM TIME '2019-04-09 18:02:52.0+00:00';

or the query variant:

SELECT * FROM t, u, v AS OF SYSTEM TIME '-4h';

?

It seems to me that there is currently no way to use this cockroach feature from within django. The code emitting BEGIN statements seems to be berried 3 dependencies down the line within psycopg.BaseConnection._get_tx_start_command, so I am not sure how to approach this elegantly.

The API could like like this for transactions (extended django.db.transaction.Atomic/.atomic):

from django_cockroachdb.transaction import atomic

with atomic(as_of_system_time="-4h"):
    pass

or like this for queries (modified QuerySet class):

Poll.objects.all().as_of_system_time("-4h")

Are there any plans to add this?

[luto]

The following works, but completely sidesteps django's transaction management. So I am sure it will lead to hard to debug issues down the road in more complex apps.

from django.db import connection

class AsOfTransaction:
    def __init__(self, as_of_system_time):
        self.as_of_system_time = as_of_system_time

    def __enter__(self):
        connection.cursor().execute("BEGIN AS OF SYSTEM TIME %s", (self.as_of_system_time,))

    def __exit__(self, exc_type, exc_value, traceback):
        if exc_type is not None:
            connection.cursor().execute("ROLLBACK")
        else:
            connection.cursor().execute("COMMIT")