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Database Transaction Time

Storing the current database transaction time in the database use the following syntax:

•    1 from canonical.database.constants import UTC_NOW
     2 
     3 person.datecreated = UTC_NOW
  

(note that you won't be able to read the value as a Python datetime object until the sync() method for the SQLObject is called, or the transaction is committed).

To store a time relative to the present time in a database column, we can make use of the fact that UTC_NOW is an "sql builder" type:

•    1 membership.dateexpires = UTC_NOW + datetime.timedelta(months=6)
  

The database transaction time can be retrieved like so:

•    1 from canonical.database.sqlbase import cursor
     2 cur = cursor()
     3 cur.execute("SELECT CURRENT_TIMESTAMP AT TIME ZONE 'UTC';")
     4 [database_now] = cur.fetchone()
  

Present Time

To create a Python datetime object that represents the present time, use the following code:

•    1 import datetime
     2 import pytz
     3 
     4 UTC = pytz.timezone('UTC')
     5 dt = datetime.datetime.now(UTC)
  

Note that the datetime.utcnow() method should not be used -- it creates a naïve datetime value, which can not be compared against other values in Launchpad.