用Date.today查询返回两天

Question

The problem is that the below query returns items from two dates, as if today / now were covering two days, whereas items from only one day should be returned with this query:

Ticket.where("DATE(created_at) = DATE(?)", Time.now.localtime.to_date).map(&:created_at)
      CACHE (0.0ms)  SELECT "tickets".* FROM "tickets"  WHERE (DATE(created_at) = DATE('2014-12-30'))
    => [Mon, 29 Dec 2014 23:15:19 UTC +00:00,
     Mon, 29 Dec 2014 23:17:48 UTC +00:00,
     Mon, 29 Dec 2014 23:18:23 UTC +00:00,
     Mon, 29 Dec 2014 23:18:28 UTC +00:00,
     Mon, 29 Dec 2014 23:19:14 UTC +00:00,
     Mon, 29 Dec 2014 23:20:08 UTC +00:00,
     Tue, 30 Dec 2014 00:11:44 UTC +00:00,
     Tue, 30 Dec 2014 00:12:12 UTC +00:00,
     Tue, 30 Dec 2014 00:14:15 UTC +00:00,
     Tue, 30 Dec 2014 00:15:35 UTC +00:00]

In the above query, Time.now.localtime.to_date returns exactly the same as Time.now.to_date , and Date.today does. This might be relevant as I am in the UTC+1 Timezone:

[50] pry(#)> Time.now
=> 2014-12-30 14:03:18 +0100
[51] pry(#)> Time.now.localtime
=> 2014-12-30 14:03:47 +0100
[52] pry(#)> Time.now.localtime.utc
=> 2014-12-30 13:03:52 UTC

Time.now equals Time.now.localtime because I have set activerecord to timestamp in local time with this code in config/application.rb :

config.active_record.default_timezone = :local

This is a db on my local machine in development environment, using sqlite3 and rails 4.1.7.

Answer 1

So what's the problem? You have set up default timezone as local, so you are getting the answer from the database, which is relevant for your timezone, since

Mon, 29 Dec 2014 23:15:19 UTC +00:00

and

Tue, 30 Dec 2014 00:15:35 UTC +00:00

are placed in the same day ( Tue, 30 Dec 2014 ) in your UTC+1 time zone

Timestamps are always in UTC by default. If you are 100% sure that your application will be used only in one timezone, and you really want to redefine the default, go to this answer: https://stackoverflow.com/a/15306358/3310560

Otherwise, if you use active_record, it's better to compare dates to themselves instead of using vanilla SQL.

Answer 2

Instead of bringing back ALL the relevant columns of the tickets table ( tickets.* ) and then stripping them down with map(&:created_at) you are much better off using pluck as in:

Ticket.where("DATE(created_at) = DATE(?)", Time.now.localtime.to_date).pluck(:created_at)

This way the DB ends up doing all the work (that it knows how to do well) and you are not bringing back all that extra data.

See more info about pluck here