# lib/generators/model.rb
module Merb::Generators
  class DatamapperModelGenerator < ComponentGenerator

    # do stuff here
    template ...

  end

  # this thing should be invisible to the end user, since it will never be called
  # directly
  add_private :datamapper_model, DatamapperModelGenerator
end

# The model generator invokes the datamapper_model generator if
# the orm is set to :datamapper
Merb::Generators::ModelGenerator.invoke :datamapper_model, :orm => :datamapper