Problem with DateTime in query

rubyonrails-talk
1

Here is a strange one for you:

I am using rails 2.1.0. I am also using the Time zones feature.

I have a User model that has many enrollments. The Enrollments model has several named scopes, one of which is today:

# This named scope is adjusted to UTC named_scope :today, :conditions => ["updated_at >= ? AND updated_at <= ?",     Time.zone.now.beginning_of_day.utc, Time.zone.now.end_of_day.utc]

If I start the server and use user.enrollments.today, I get back today's enrollments, as you would expect. Once tomorrow arrives, and I utilize the same query, I get yesterday's enrollments. I have put the server's logger in debug mode to capture the queries and sure enough, it is asking for yesterday's enrollments.

First day's log:

Processing CoursesController#show (for 66.249.102.37 at 2008-10-07 13:24:35) [GET] ... maxed_out_hours_for_today?() begin calculate_hours_today() begin hours_today: 0.0   e[4;36;1mEnrollment Load (0.001272)e[0m e[0;1mSELECT * FROM `enrollments` WHERE (`enrollments`.user_id = 213) AND (((updated_at >= '2008-10-07 04:00:00' AND updated_at <= '2008-10-08 03:59:59') AND (mode = 'evaluated')) AND (exam_id IS NULL)) e[0m Found 6 enrollments for user **********

Second day's log:

Processing CoursesController#show (for 66.249.102.37 at 2008-10-08 07:22:19) [GET] ...   e[4;35;1mEnrollment Load (0.001750)e[0m e[0mSELECT * FROM `enrollments` WHERE (`enrollments`.user_id = 213) AND (((updated_at >= '2008-10-07 04:00:00' AND updated_at <= '2008-10-08 03:59:59') AND (mode = 'evaluated')) AND (exam_id IS NULL)) e[0m Found 6 enrollments for user *************

Notice that the dates are the same on both days. This makes no sense because Time.zone.now.beginning_of_day.utc and Time.zone.now.end_of_day.utc are what is being used in teh named_scope. It does not seem to be a time zone issue, as we are in CDT, which is -5 from UTC right now. The second day's query is outside of the possible 5 hour overlap if I was making a mistake.

Does anyone have any idea what could be causing this?

2

The Time.zone.now is evaluated precisely once: when the model is loaded. Use a lambda (see the section on procedural scopes in the api docs) to do something like

named_scope :today, lambda { :conditions => stuff here is evaluated each time the scope is accessed }

Fred

3

Ryan Bates' screencast on this topic - #108 named_scope - RailsCasts - has more details about delaying evaluation of the condition with a lambda (including optional argument).

How weird, I literally just watched his screencast before reading this question.