How to convert time to date in the local timezone during query

问题

We have a very simple payments model with the default "created_at" datetime field that we have to search in a date range so I did this:

>> Payment.all(:conditions => 
              ["Date(payments.created_at) >= ? and 
                Date(payments.created_at) <= ?", start_date, end_date])

I'm having an issue with the Date function. For example

>> Payment.find(2577).created_at
=> Thu, 15 Dec 2011 18:15:00 UTC +00:00

But

>> Payment.find(2577).created_at.localtime
=> Fri Dec 16 01:15:00 +0700 2011

So when we search for payments on Dec 16 we don't get any results since Date(payments.created_at) converts the UTC time to date which gets converted to Dec 15.

Is it possible to modify Date(payments.created_at) so that it searches for dates the local timezone instead? We are using Rails 2.3.5 and postgresql.

回答1:

Finally got it to work! Not very pretty (and I'm hoping there's a cleaner solution) but this worked:

>> Payment.all(:conditions => 
              ["Date((payments.created_at at time zone 'UTC') 
                at time zone :timezone) >= :start_date and 
                Date((payments.created_at at time zone 'UTC') 
                at time zone :timezone) <= :end_date",
               :start_date => start_date, :end_date => end_date, 
               :timezone => 'Asia/Katmandu'])

Not really liking having to do this though:

Date((payments.created_at at time zone 'UTC') at time zone 'Asia/Katmandu')

How come postgresql doesn't let you just do this?

Date(payments.created_at at 'Asia/Katmandu')

回答2:

Can you just run .localtime on your start_date and end_date? Something like:

Payment.all(:conditions => 
  ["Date(payments.created_at) >= ? and 
    Date(payments.created_at) <= ?", start_date.localtime, end_date.localtime])

You might also be able to set your local timezone in config/environment.rb file:

config.time_zone = 'UTC'

来源：https://stackoverflow.com/questions/8652623/how-to-convert-time-to-date-in-the-local-timezone-during-query

标签

sql

ruby-on-rails

postgresql

activerecord

timezone