Generating your own thumbnails with acts_as_attachment

Generating your own thumbnails with acts_as_attachment:

As per my blog post, here’s how to create your own thumbnails using acts_as_attachment.

Rick Olson’s acts_as_attachment plugin is the shit when it comes to handling file uploads in Rails, but it lacks the

:crop

option that the file_column plugin does.

If you’re looking for flickr-style square thumbnails you’ll have to do the thumbnail generation yourself.

Luckily for us Rick provides an

after_attachment_saved

callback which gets called when a photo gets saved. We can use this hook to generate our own thumbnails rather than using acts_as_attachment’s pre-baked

:thumbnails

option. The only gotcha is that the hook also gets called when the thumbnail itself is saved, so you have to check the

parent_id

before going ahead.

class Photo < ActiveRecord::Base
  THUMBS = { :profile => 150, :medium => 75, :tiny => 25 }

  belongs_to :person
  acts_as_attachment :storage => :file_system,
                     :content_type => :image

  validates_as_attachment

  # We handle our own thumbnail generation
  after_attachment_saved do |photo|
    if photo.parent_id.nil?
      THUMBS.each_pair do |file_name_suffix, size|
        thumb = thumbnail_class.find_or_initialize_by_thumbnail_and_parent_id(file_name_suffix.to_s, photo.id)
        resized_image = photo.crop_resized_image(size)
        unless resized_image.nil?
          thumb.attributes = {
            :content_type    => photo.content_type, 
            :filename        => photo.thumbnail_name_for(file_name_suffix.to_s), 
            :attachment_data => resized_image
          }
          thumb.save!
        end
      end
    end    
  end

  def crop_resized_image(size)
    thumb = nil
    with_image do |img|
      thumb = img.crop_resized(size, size)
    end
    thumb
  end
end