Paperclip is popular gem used in rails project to provide attachment feature in your model. It is very flexible and easy to use.
I mostly use paperclip for my project if I need to provide attachment feature. You can get more detail about how to use paperclip from github repo.
I was working on project in which I have used RailsAdmin for administration. I was having a situation where I need to remove feature of attachment from model. With a view of changes, I just removed attachment code from my model which is :
I was trying to access model from RailsAdmin and faced error saying
undefined method `attachment_definitions'
After checking all aspects, I get to know that I forget to remove fields from database / schema.rb . To do that I have generated new migration file which removes that fields from database and modify schema.rb. My migration was containing following code :
remove_attachment :table_name, :attachment_attr_name
For example : remove_attachment :users, :avatar
I ran that migration with rake db:migrate and it fixes the problem.
Hope that helps!!!