Parsing dates and times in Ruby and Rails

August 11, 2010

Out of the box, Rails’ date_select input type and other date/time-related times are a bit ugly and not very user-friendly—just a series of pulldown menus from which to select the month, day, year, hour, minute, and so on. You can pretty these up using a number of calendar-related plugins, notably by using Javascript, but there’s another way you can make date and time more user-friendly. I like going with a basic text input, let my users enter dates like “tomorrow,” “8/12/10,” “August 12,” or “next Thursday,” then parsing the entries before storing them in the database.

In this crash course in natural date/time parsing in Ruby, we’re going to look at two gems called Chronic and Chronic Duration. These gems handle almost any date or time format your users throw at them and store them in database-friendly formats without the need for Javascript on the client side or hand-coded Ruby on the server side.

Chronic

Let’s start with Chronic for parsing date/time values into something you can store in a database. First, install the gem:

  $ gem install chronic

Chronic’s usage is very straightforward. Let’s fire up irb or script/console to have a look:

  > require 'rubygems'
    => true
  > require 'chronic'
    => true
  > Chronic::parse('tomorrow')
    => Thu Aug 12 12:00:00 -0500 2010
  > Chronic::parse('next saturday')
    => Sat Aug 14 12:00:00 -0500 2010
  > Chronic::parse('8/12/10 3pm')
    => Thu Aug 12 15:00:00 -0500 2010

So rather than requiring users to use Rails’ default pulldown-based date picker, or enter data in forced formats (like MM/DD/YYYY), or click through Javascript-based calendars, your app can be smart about parsing the entered date into something meaningful to the server. For that matter, you can use it in conjunction with a Javascript calendar (like the datepicker in JQuery UI) for further functionality.

Chronic Duration

Say you’re developing a cooking site or project management tool and want to allow users to enter spans of time like “35 minutes,” “1 hour 15 minutes,” “1:30,” or “2 days” and store them in a consistent format. Enter Chronic Duration—it works like Chronic, but for stretches of time as opposed to actual dates or times. After parsing the entry, the duration is stored in the database as the number of seconds. First, install the gem:

  $ gem install chronic_duration

Let’s look at it in action using irb (or script/console):

  > require 'chronic_duration'
    => true
  > ChronicDuration::parse('15 minutes')
    => 900
  > ChronicDuration::parse('1:15') # note this is MM:SS
    => 75
  > ChronicDuration::parse('45s')
    => 45

And so on. Chronic Duration also provides an output method:

  > ChronicDuration::output(75, :format => :short)
    => "1m 15s" 
  > ChronicDuration::output(75, :format => :long)
    => "1 minute 15 seconds" 
  > ChronicDuration::output(75, :format => :chrono)
    => "1:15"

Using Chronic and Chronic Duration in Rails

Experimenting with the gems in the console is one thing, but how do we put them to use in a Rails application? Here’s how I do it. Going back to the idea of a project tracker, say I’ve got a model named Task with a due date and an estimated time field. It might look like this:

  # app/models/task.rb

  require 'chronic'
  require 'chronic_duration'

  class Task < ActiveRecord::Base
    attr_accessible :name, :description, :due_at, :estimated_time
    
    def before_save
      self.due_at = Chronic::parse(self.due_at_before_type_cast) if attribute_present?("due_at")
      self.estimated_time = ChronicDuration::parse(self.estimated_time_before_type_cast) if attribute_present?("estimated_time")
    end
  end

Don’t forget to include Chronic and Chronic Duration in your Gemfile or config/environment.rb file, and restart your application.

There are a few ways you could use ChronicDuration::output in your application’s views—you could either override the accessor in the model by adding something like

  # app/models/task.rb
  
  def estimated_time
    ChronicDuration.output(read_attribute(:estimated_time), :format => :long)
  end

or use it in a view helper along the lines of

  # app/helpers/tasks_helper.rb
  
  require 'chronic_duration'
  
  module TasksHelper
    def display_time(time = 0)
      ChronicDuration.output(time, :format => :long)
    end
  end

and use the helper in your views. It depends on what you need to do with the data, so experiment within your application to see what works best.

Chronic doesn’t include a function to return a date value in a pretty format—just use Ruby’s strftime method to handle that.

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