This snippets shows you how to create a daemon process out of an ordinary Ruby script.

First you’ll need the daemons gem:

   1  gem install daemons

Then you’ll need the daemon script, for example daemon.rb:

   1  require 'rubygems'
   2  require 'daemons'
   3  
   4  pwd  = File.dirname(File.expand_path(__FILE__))
   5  file = pwd + '/../lib/background_service.rb'
   6  
   7  Daemons.run_proc(
   8    'background_service', # name of daemon
   9  #  :dir_mode => :normal
  10  #  :dir => File.join(pwd, 'tmp/pids'), # directory where pid file will be stored
  11  #  :backtrace => true,
  12  #  :monitor => true,
  13    :log_output => true
  14  ) do
  15    exec "ruby #{file}"
  16  end

Change the file variable to point to the script you want to daemonize and your good to go.

You can now execute the daemon.rb script without parameters to get a list of available commands for controlling the daemon process:

   1  ERROR: no command given
   2  
   3  Usage: lib/background_service.rb <command> <options> -- <application options>
   4  
   5  * where <command> is one of:
   6    start         start an instance of the application
   7    stop          stop all instances of the application
   8    restart       stop all instances and restart them afterwards
   9    run           start the application and stay on top
  10    zap           set the application to a stopped state
  11  
  12  * and where <options> may contain several of the following:
  13  
  14      -t, --ontop                      Stay on top (does not daemonize)
  15      -f, --force                      Force operation
  16  
  17  Common options:
  18      -h, --help                       Show this message
  19          --version                    Show version

Simple example of how to use the named_scope feature:

   1  class Feed < ActiveRecord::Base
   2   
   3    named_scope :active, :conditions => "(active = 1)"
   4    named_scope :stale,  :conditions => ["last_updated > ?", 30.minutes.ago.to_s(:db)]

Usage:

   1  Feed.active # return the active feeds

Chaining is also possible:

   1  Feed.active.stale # return the feeds that need to be updated

   1  <input name="authenticity_token" value="<%= form_authenticity_token %>" type="hidden" />

or

   1  <%= token_tag %> 

Use this snippet to add a watermark to an image, after the image is uploaded:

   1  class Image
   2    .
   3    has_attachment ...
   4    .
   5    .
   6    after_attachment_saved do |record|    
   7      # Don't add watermarks to thumbnails
   8      if record.thumbnail.nil?
   9        full_path = File.join(RAILS_ROOT, 'public/', record.public_filename)
  10        
  11        img = MiniMagick::Image.from_file(full_path)
  12        
  13        width = img[:width]
  14        height = img[:height]
  15        
  16        if width > 150 && height > 150
  17          img.combine_options do |c|
  18            c.gravity 'SouthWest'
  19            # This is RAILS_ROOT/images/watermark.gif
  20            c.draw "image Over 0,0 0,0 \"images/watermark.gif\""
  21          end
  22  
  23          img.write(full_path)
  24          
  25        end
  26      end
  27      
  28    end

Note that after_attachment_saved is a callback added by attachment_fu, use after_save if you’re not using attachment_fu.

   1  require 'rubygems'
   2  require 'mini_magick'
   3  
   4  img = MiniMagick::Image.from_file("jpeg.jpg")
   5  
   6  img.combine_options do |c|
   7    c.gravity 'Southwest'
   8    c.draw 'text 10,10 "whatever"'
   9    c.font '-*-helvetica-*-r-*-*-18-*-*-*-*-*-*-2'
  10    c.fill("#FFFFFF")
  11  end
  12  
  13  img.write("new.jpg")