选用资源报错

app/models/attachment.rb

@@ -19,7 +19,7 @@ class Attachment < ApplicationRecord
   scope :contains_only_project,         -> { where(container_type: 'Project') }
   scope :contains_course_and_project,   -> { contains_only_course.or(contains_only_project) }
   scope :mine,                          -> (author_id) { where(author_id: author_id) }
-  scope :simple_columns,                -> { select(:id, :filename, :filesize, :created_on, :cloud_url, :author_id) }
+  scope :simple_columns,                -> { select(:id, :filename, :filesize, :created_on, :cloud_url, :author_id, :content_type) }
   scope :search_by_container,           -> (ids) {where(container_id: ids)}
 
   validates_length_of :description, maximum: 100