add worker to get mime type from dspace

app/models/learning_object.rb

@@ -47,8 +47,11 @@ class LearningObject < ActiveRecord::Base
 
   def default_attachment
     return attachment unless attachment.nil?
+
     unless attachments.blank?
-      update(attachment: attachments.first)
+      at = attachments.where(bundle_name: 'ORIGINAL').first
+      at = attachments.first if at.nil?
+      update(attachment: at)
       return attachment
     end
     nil

app/models/learning_object/attachment.rb

 class LearningObject::Attachment < ActiveRecord::Base
   belongs_to :learning_object
 
-  has_attached_file :thumbnail, styles: {medium: "530x300", small: "250x140"}
-  validates_attachment_content_type :thumbnail, :content_type => ["image/jpg", "image/jpeg", "image/png", "image/gif"]
+  scope :unknown_mime_type, ->() { where(format: 'Unknown') }
+
+  has_attached_file :thumbnail, styles: { medium: '530x300', small: '250x140' }
+  validates_attachment_content_type :thumbnail, content_type: ['image/jpg', 'image/jpeg', 'image/png', 'image/gif']
 end

app/workers/bitstream_mime_worker.rb

+class BitstreamMimeWorker
+  include Sidekiq::Worker
+
+  def perform(id)
+    attachment = LearningObject::Attachment.find(id)
+    client = DspaceService.create_client
+
+    begin
+      file = client.bitstreams.retrieve(id: attachment.id_dspace).open
+      mime = MimeMagic.by_magic(file)
+      attachment.update(format: mime.mediatype, mime_type: mime.type) unless mime.blank?
+    ensure
+      file.close unless file.nil?
+    end
+  end
+end

lib/tasks/attachments.rake

+namespace :attachments do
+  desc 'Set mime type where is unknown'
+  task set_unknown: :environment do
+    LearningObject::Attachment.unknown_mime_type.find_each { |a| BitstreamMimeWorker.perform_async(a.id) }
+  end
+end