Set custom Paperclip attachments style based on specific attribute extra value.

PaperclipDynamicStyle.rb

class Attachment < ApplicationRecord
  
  has_attached_file :file,
                    styles: ->(a) { a.instance.paperclip_styles },
                    path: 'public/system/:class/:id/:style_:filename',
                    url: '/system/:class/:id/:style_:filename'

  validates_attachment_presence :file
  
  def paperclip_styles
    case typology
    when 'profile'
      {
        thumb: '200x200>'
      }
    when 'cover'
      {
        thumb: '200x200>'
        medium: '600x400>'
      }
    when 'post_image'
      {
        medium: '600x400>'
      }
    else
      {}
    end
  end
  
  after_create do
    file.reprocess!
  end
  
end