# Install the google-appengine gem
$ sudo gem install google-appengine

# Check gem sources for datamapper
$ gem sources

# Add datamapper to your gem sources (if missing)
$ appcfg.rb gem sources --add http://gems.datamapper.org

# install the gems into your application
$ appcfg.rb gem install sinatra dm-appengine

# Start the development server
$ dev_appserver.rb .

# Create an application-id at appspot.com:
> http://appengine.google.com/start/createapp

# Replace the application-id in config.ru
> :application => "your-app-id"

# Upload to App Engine
$ appcfg.rb update .