A paperclip compatible carrierwave uploader

app/uploaders/picture_uploader.rb

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+# encoding: utf-8
+
+class PictureUploader < CarrierWave::Uploader::Base
+  include CarrierWave::MiniMagick
+  include CarrierWave::Compatibility::Paperclip
+
+  def paperclip_path
+    "system/#{object_class_name}/#{extra_store_dir}/#{id_partition}/:style/:basename.:extension"
+  end
+
+  def object_class_name
+    model.class.to_s.underscore.pluralize
+  end
+
+  # compatibility with our paperclip storage paths..
+  def extra_store_dir
+    case object_class_name
+    when 'conferences'
+      'logos'
+    when 'lodgings'
+      'photos'
+    when 'sponsors'
+      'logos'
+    when 'venues'
+      'photos'
+    else mounted_as
+    end
+  end
+
+  # Returns the id of the instance in a split path form. e.g. returns
+  # 000/001/234 for an id of 1234. Stolen from paperclip...
+  def id_partition
+    ('%09d'.freeze % model.id).scan(/\d{3}/).join('/'.freeze)
+  end
+
+  # Override the directory where uploaded files will be stored.
+  # This is a sensible default for uploaders that are meant to be mounted:
+  def store_dir
+    "system/#{object_class_name}/#{mounted_as}/#{model.id}"
+  end
+
+  # Create different versions of your uploaded files:
+  version :large do
+    process resize_to_fit: [300, 300]
+  end
+
+  version :thumb, from_version: :large do
+    process resize_to_fit: [100, 100]
+  end
+
+  version :first, if: :sponsor?
+  version :first do
+    process resize_to_fill: [320, 180]
+  end
+
+  version :second, if: :sponsor?
+  version :second, from_version: :first do
+    process resize_to_fill: [320, 150]
+  end
+
+  version :others, if: :sponsor?
+  version :others, from_version: :second do
+    process resize_to_fill: [320, 120]
+  end
+
+  # Add a white list of extensions which are allowed to be uploaded.
+  # For images you might use something like this:
+  def extension_white_list
+    %w(jpg jpeg gif png)
+  end
+
+  def content_type_whitelist
+    %r{/image\//}
+  end
+
+  private
+
+  def sponsor?(_picture)
+    object_class_name == 'sponsors'
+  end
+end

config/initializers/carrierwave.rb

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+CarrierWave.configure do |config|
+  config.storage = :file
+  config.cache_dir = "#{Rails.root}/tmp/uploads"
+end