How do you do relative time in Rails?

Question

Sounds like you're looking for the time_ago_in_words method (or distance_of_time_in_words), from ActiveSupport. Call it like this:

<%= time_ago_in_words(timestamp) %>

I've written this, but have to check the existing methods mentioned to see if they are better.

module PrettyDate
  def to_pretty
    a = (Time.now-self).to_i

    case a
      when 0 then 'just now'
      when 1 then 'a second ago'
      when 2..59 then a.to_s+' seconds ago' 
      when 60..119 then 'a minute ago' #120 = 2 minutes
      when 120..3540 then (a/60).to_i.to_s+' minutes ago'
      when 3541..7100 then 'an hour ago' # 3600 = 1 hour
      when 7101..82800 then ((a+99)/3600).to_i.to_s+' hours ago' 
      when 82801..172000 then 'a day ago' # 86400 = 1 day
      when 172001..518400 then ((a+800)/(60*60*24)).to_i.to_s+' days ago'
      when 518400..1036800 then 'a week ago'
      else ((a+180000)/(60*60*24*7)).to_i.to_s+' weeks ago'
    end
  end
end

Time.send :include, PrettyDate

Just to clarify Andrew Marshall's solution for using time_ago_in_words
(For Rails 3.0 and Rails 4.0)

If you are in a view

<%= time_ago_in_words(Date.today - 1) %>

If you are in a controller

include ActionView::Helpers::DateHelper
def index
  @sexy_date = time_ago_in_words(Date.today - 1)
end

Controllers do not have the module ActionView::Helpers::DateHelper imported by default.

N.B. It is not "the rails way" to import helpers into your controllers. Helpers are for helping views. The time_ago_in_words method was decided to be a view entity in the MVC triad. (I don't agree but when in rome...)

What about

30.seconds.ago
2.days.ago

Or something else you were shooting for?

You can use the arithmetic operators to do relative time.

Time.now - 2.days 

Will give you 2 days ago.

Something like this would work.

def relative_time(start_time)
  diff_seconds = Time.now - start_time
  case diff_seconds
    when 0 .. 59
      puts "#{diff_seconds} seconds ago"
    when 60 .. (3600-1)
      puts "#{diff_seconds/60} minutes ago"
    when 3600 .. (3600*24-1)
      puts "#{diff_seconds/3600} hours ago"
    when (3600*24) .. (3600*24*30) 
      puts "#{diff_seconds/(3600*24)} days ago"
    else
      puts start_time.strftime("%m/%d/%Y")
  end
end

Since the most answer here suggests time_ago_in_words.

Instead of using :

<%= time_ago_in_words(comment.created_at) %>

In Rails, prefer:

<abbr class="timeago" title="<%= comment.created_at.getutc.iso8601 %>">
  <%= comment.created_at.to_s %>
</abbr>

along with a jQuery library http://timeago.yarp.com/, with code:

$("abbr.timeago").timeago();

Main advantage: caching

http://rails-bestpractices.com/posts/2012/02/10/not-use-time_ago_in_words/