add attachment model and add paperclip

app/models/attachment.rb

@@ -0,0 +1,10 @@
+class Attachment < ActiveRecord::Base
+  belongs_to :todo, touch: true
+
+  has_attached_file :file,
+    url:  '/:class/:id/:basename.:extension',
+    path: ":rails_root/db/assets/#{Rails.env}/:class/:id/:basename.:extension"
+
+  do_not_validate_attachment_file_type :file
+  # validates_attachment_content_type :file, :content_type => ["text/plain"]
+end

app/models/todo.rb

@@ -25,6 +25,8 @@ class Todo < ActiveRecord::Base
   has_many :pending_successors, -> {where('todos.state = ?', 'pending')}, :through => :predecessor_dependencies,
     :source => :successor
 
+  has_many :attachments, dependent: :delete_all
+
   # scopes for states of this todo
   scope :active, -> { where state: 'active' }
   scope :active_or_hidden, -> { where "todos.state = ? OR todos.state = ?", 'active', 'project_hidden' }