thinking_sphinx_tweaks_for_sinatra.rb

# Add that to your app make, after you define the sinatra env.
Thread.current[:thinking_sphinx_environment] = Sinatra::Application.environment

# When requiring TS add a new task to properly generate the config file

require 'thinking_sphinx'
require 'thinking_sphinx/tasks'

namespace :thinking_sphinx do
  namespace :my_app do
    desc "Generate the Sphinx configuration file using Thinking Sphinx's settings"
    task :setup => :app_env do
      Thread.current[:thinking_sphinx_environment] = Sinatra::Application.environment
      config = ThinkingSphinx::Configuration.instance
      config.reset(Sinatra::Application.root)
      puts "Generating Configuration to #{config.config_file}"
      config.build
    end
  end
end

The only think you really need to care about is:

Thread.current[:thinking_sphinx_environment] = Sinatra::Application.environment
ThinkingSphinx::Configuration.instance.reset(Sinatra::Application.root)

If you set that up in your main file before loading your ts tasks, you are good to go.