Question

(I’m using Rails 3.2.3 on Ruby MRI 1.9.2)

Everything is stored centrally in UTC. This is good. Each User has a ‘timezone’ property. My ApplicationController has a before filter to adjust Time.zone to the User’s stored timezone. This is also good.

Given the above, if my User completes a datetime select with a time, that time is expected to be in Time.zone and Rails will automatically adjust and save this as UTC. This too, is good.

Now: I wish to enable my Users to fill out a time in another time zone and then have it stored as UTC. However, Rails is expecting the completed date time select to have been filled out in the (previously set by ApplicationController) Time.zone. Therefore Rails adjusts to UTC incorrectly.

How do I achieve my goal of saving a time that has been input as being in a third time zone?

Illustration:

My usage scenario is a User in Florida adjusting a date for a Document belonging to a Hotel on the West Coast. They are looking to enter a time for the West Coast.

I’m using jQuery to style text boxes with a styled picker, so I have a method to output a string to the text box:

<%= f.text_field(:created_at, :value => adjusted_to_hotel_time(@document.created_at), :class => 'text datetime_picker') %>

def adjusted_to_hotel_time(time)
  time.in_time_zone(@current_hotel.timezone).to_s(:admin_jquery) # formatted for the jQuery datetime_picker text fields.
end

This is working perfectly, but Rails adjusts to UTC incorrectly when the @document is saved. I don’t know what I don’t know – how can I ‘tag’ the data entered in that field as being in @current_hotel.timezone, so that Rails will offset to UTC correctly when it saves the parent object?

Answer 1

Cracked it!

Basically, the string that is submitted to params is representing a time in a Hotel’s timezone. We have to use the built in ‘use_zone’ method to temporarily set the global Time.zone to that Hotel’s.

We then pass the method a block where we produce the value that Rails is expecting, by using the timezone of the Hotel, rather than the User. That means that Rails’ conversion to UTC results in the correct time in the db – as the time entered on the form has been converted to the Users timezone. The offsets have cancelled each other out, effectively.

@document.created_at = Time.use_zone(@current_hotel.timezone) {Time.zone.parse("#{params[:document][:created_at]}").in_time_zone(@current_hotel.timezone)}

We’re basically changing the timezone of the Time object here without converting the actual time of that Time object when the timezone changes. (Good luck parsing that sentence!)

This looks to be working fine for me, but I’ve been looking at this for too long and I’d love to see a better way/more Rails-ey way of doing this!