Rolls back database to migration level of the previously deployed release

gistfile1.rb

before "deploy:rollback:revision", "deploy:rollback_database"

  desc "Rolls back database to migration level of the previously deployed release"
  task :rollback_database, :roles => :db, :only => { :primary => true } do
    if releases.length < 2
      abort "could not rollback the code because there is no prior release"
    else
      rake = fetch(:rake, "rake")
      rails_env = fetch(:rails_env, "production")
      migrate_env = fetch(:migrate_env, "")
      migrate_target = fetch(:migrate_target, :latest)
      run "cd #{current_path}; #{rake} RAILS_ENV=#{rails_env} #{migrate_env} db:migrate VERSION=`cd #{File.join(previous_release, 'db', 'migrate')} && ls -1 [0-9]*_*.rb | tail -1 | sed -e s/_.*$//`"
    end
  end