Grip is a MongoMapper GridFS Attachment gem, and is a dependency for grip-rails.

GridFile adds a route for /images/grid/[file_name] this route will fetch images attached to a MongoMapper::Document with Grip.

Alternately, this route checks for /images/grid/resize_[width]x[height]_[file_name] and will serve up, and cache, an image at the requested file dimensions.

To help with these dynamic url, there is a #url method placed on Grip::Attachment. (See grip documentation).

Set up a grid_attachment:

class Doc
  include MongoMapper::Document
  include Grip::HasAttachment
  has_grid_attachment :image, :variants => {:thumb => {:width=>50,:height=>50}}
end

Then you can call #url:

puts @doc.image.url 
=> /images/grip/doc/12345678910/image/file_name.jpg

And when a variant is passed in:

puts @doc.image.url(:thumb) 
=> /images/grip/doc/12345678910/image/resize_50X50_file_name.jpg