Rails AR查询中的时间比较问题

Question

I'm running Rails 3.0.4 with a PostgreSQL Database and i created a DateTime field called ordered_at .

I set it by creation with Time.now and i want to query the ordered_at field with something like where("ordered_at > ?", params[:later_than] , but if I put later than with something like 1.minute.from_now, I'm getting results where no results should be.

In Detail: ordered_at is 2011-03-08 11:11:49 and params[:later_than] is 2011-03-08 11:09:58 UTC .

I think that is because of the time zone in the Time object, which doesn't exists in the database (The ordered_At field is a timestamp without time zone Datatype).

Does anyone had the same problem and can help me?

Answer 1

Fixed it. The root of evil was in my fixtures.

You have to set times in your fixtures like that:

  ordered_at: <%= (30.minutes.ago).iso8601 %>

otherwise you will get the timezone of the database/server

Answer 2

The thing you have to remember is Rails store the time in your database in UTC. Rails convert the time into UTC and sets it as the standard to look at in the database. So if you have params[:later_than] as 2011-03-08 11:11:49 UTC or any time for that matter with any time zone, Rails will convert it into UTC time zone before inserting into the SQL query. If you are saving Time.now into the database, Time.now will be the server time or local machine time with the time zone in which the machine is set. Before saving to database, Rails will convert it to UTC and save it. So, at database level everything will be converted to UTC and then will be compared so avoiding confusion.