configures padrino to use config/mongoid.yml

database.rb

# config/database.rb

config_file = Padrino.root("config", "mongoid.yml")
if File.exists?(config_file)
  settings = YAML.load(ERB.new(File.read(config_file)).result)[Padrino.env.to_s]
  ::Mongoid.from_hash(settings) if settings.present?
end

mongoid.yml

# config/mongoid.yml

options: &options
  parameterize_keys: false

defaults: &defaults
  host: localhost
  # slaves:
  #   - host: slave1.local
  #     port: 27018
  #   - host: slave2.local
  #     port: 27019

development:
  <<: *defaults
  <<: *options
  database: tweetup_dev

test:
  <<: *defaults
  <<: *options
  database: tweetup_test

production:
  <<: *options
  uri: <%= ENV['MONGOHQ_URL'] %>
  database: tweetup

or just remove database.rb and put
Mongoid.load!("config/mongoid.yml")
at boot.rb