Delayed image processing with CarrierWave

carrierwave.rb

CarrierWave.configure do |config|
 ...
end

Mongoid::Document::ClassMethods.send(:include, DelayedImageProcessing)

module CarrierWave

  # http://sleeplesscoding.blogspot.com/2011/09/recreate-single-version-of.html
  # Note: is_processing_delayed should be set before calling recreate_version! if the version depends on it.
  module Uploader
    module Versions
      def recreate_version!(version)
        already_cached = cached?
        cache_stored_file! if !already_cached
        send(version).store!
        if !already_cached && @cache_id
          tmp_dir = File.expand_path(File.join(cache_dir, cache_id), CarrierWave.root)
          FileUtils.rm_rf(tmp_dir)
        end
      end
    end
  end
  
  # Avoid overwriting original filename in delayed-processing.
  module Mount
    class Mounter
      def write_identifier
        if remove?
          record.write_uploader(serialization_column, '')
        elsif uploader.identifier.present? &&
          (!uploader.respond_to?(:is_processing_immediate?) || uploader.is_processing_immediate?)
          record.write_uploader(serialization_column, uploader.identifier)
        end
      end
    end
  end
end

delayed_image_processing.rb

# A model mounting an uploader with delayed processing should pass delayed: true to the uploader:
#     mount_uploader :image, ArtistUploader, delayed: true
# ...and the uploader's versions should be conditional on is_processing_delayed?:
#     version :small, :if => :is_processing_delayed? {...}
module DelayedImageProcessing

  def mount_uploader(column, uploader=nil, options={}, &block)
    delay = options.delete(:delayed)
    super
    if delay
      process_in_background(column)
      if uploader && !uploader.include?(DelayedImageProcessing::UploaderMethods)
        uploader.send(:include, DelayedImageProcessing::UploaderMethods)
      end
    end
  end
  
  def process_in_background(column = :image)
    after_save :"queue_recreate_#{column}_versions!", :if => :"#{column}_file_changed"
    attr_accessor :"#{column}_file_changed"
    define_model_callbacks :image_processing

    class_eval <<-RUBY, __FILE__, __LINE__+1
      def queue_recreate_#{column}_versions!
        self.#{column}_file_changed = false
        self.delay.recreate_#{column}_versions!
      end
      
      def recreate_#{column}_versions!
        begin
          #{column}.is_processing_delayed = true
          _run_image_processing_callbacks do
            #{column}.recreate_versions!
          end
        ensure
          #{column}.is_processing_delayed = false
        end
      end
      
      def #{column}=(obj)  # track when a new file has been set
        super(obj)
        self.#{column}_file_changed = true
      end
    RUBY
    
  end
  
  module UploaderMethods
    def is_processing_delayed?(img = nil)
      !! @is_processing_delayed
    end

    def is_processing_immediate?(img = nil)
      ! is_processing_delayed?
    end

    def is_processing_delayed=(value)
      @is_processing_delayed = value
    end
  end

end

All credit for this goes to @Jaghion, (c) Art.sy MIT License. To use add the code from the top gist to config/initializers/carrierwave.rb and place delayed_image_processing.rb somewhere in lib.

I guess the monkey patch is not necessary anymore, as

instance = MyUploader.new
instance.recreate_versions!(:thumb, :large)

is now part of carrierwave. Am I missing something else?

How can i adapt this to active record?

I put on a gem together to work with delayed jobs and active record, check it out https://github.com/IcaliaLabs/carrierwave_versions_backgrounder and let me know if you find it useful!

I get this error whenever I'm trying to upload an image - undefined method `delay'
I'm using Mongoid 5.1.0 and uploading the image to Carrierwave using JSON API using this link-
https://gist.github.com/ifightcrime/9291167a0a4367bb55a2

My carrierwave.rb file looks like this -

CarrierWave.configure do |config| #commented configuration for connecting to S3 bucket in production mode end

followed by your code above.

Can you please point out to what I'm doing wrong? Thank you!