Check whether migrations need to be run without requiring the whole app

db_uptodate.rake

namespace :db do
  task :uptodate do
    if pending_migrations.blank?
      puts "Migrations are up-to-date"
    else
      puts "The following migrations are pending:"
      puts pending_migrations.map { |mp| "%s\t\t%s" % [ mp.version, mp.name ] }.join("\n")
    end
  end
  
  # Only run this from a single host
  task :migrate_unless_uptodate do
    Rake::Task['db:migrate'].invoke unless pending_migrations.blank?
  end
  
  def pending_migrations
    return @pending_migrations if @pending_migrations
    require 'active_record'
    ActiveRecord::Base.configurations = YAML.load_file('config/database.yml')
    ActiveRecord::Base.establish_connection
    @pending_migrations = ActiveRecord::Migrator.new(:up, 'db/migrate').pending_migrations
  end
end