The MongoDB classes do not come with default generators for Rails applications. In order to use the rails generate commands, you can use the indirect rails3-generators project available at https://github.com/indirect/rails3-generators/#readme
Installation:
1. Download the generators into your application’s lib folder:
cd myapp
git clone git://github.com/indirect/rails3-generators.git lib/generators
2. Install the rails3-generators gem
gem install rails3-generators
3. Add this to your project’s Gemfile
gem 'rails3-generators'
Usage:
rails generate model ModelName --orm=mongo_mapper