How do I convert a time to users time zone in Rails

Question

I set the local timezone in Rails with this javascript function in my layout:

<script type="text/javascript" charset="utf-8">
        <% unless session[:timezone_offset] %>
            $.ajax({
           url: '/main/timezone',
           type: 'GET',
           data: { offset: (new Date()).getTimezoneOffset() }
            });
        <% end %>
    </script>

where this is the receiving function:

# GET /main/timezone                                                     AJAX
  #----------------------------------------------------------------------------
  def timezone
    #
    # (new Date()).getTimezoneOffset() in JavaScript returns (UTC - localtime) in
    # minutes, while ActiveSupport::TimeZone expects (localtime - UTC) in seconds.
    #
    if params[:offset]
      session[:timezone_offset] = params[:offset].to_i * -60
      ActiveSupport::TimeZone[session[:timezone_offset]]
    end
    render :nothing => true
  end

And then I have the offset in my session, so I do something like this to show a time:

<%= (@product.created_at + session[:timezone_offset]).strftime("%m/%d/%Y %I:%M%p") + " #{ActiveSupport::TimeZone[session[:timezone_offset]]}" %>

Is all of this really necessary in Rails 3? I think the first two code blocks may be, but the third seems a bit excessive...

Answer 1

You can set current time zone and it will be remembered for all operations. It can be done in a before_filter of some very high controller, like AppController. For example

class ApplicationController < ActionController::Base
  before_filter :set_zone_from_session

  private

  def set_zone_from_session
    # set TZ only if stored in session. If not set then the default from config is to be used
    # (it should be set to UTC)
    Time.zone = ActiveSupport::TimeZone[session[:timezone_offset]] if session[:timezone_offset]
  end

end

Probably it doesn't look better on the first sight - but it will influence all views so no need for any conversions there.