rails 4 rails 4.0.0.rc1 mountable engine rake db:migrate

namespace :db do
  task :load_config do
    ActiveRecord::Base.configurations = ActiveRecord::Tasks::DatabaseTasks.database_configuration || {}
    ActiveRecord::Migrator.migrations_paths = ActiveRecord::Tasks::DatabaseTasks.migrations_paths
    if defined?(ENGINE_PATH) && engine = Rails::Engine.find(ENGINE_PATH)
      if engine.paths['db/migrate'].existent
        ActiveRecord::Migrator.migrations_paths += engine.paths['db/migrate'].to_a
      end
    end
  end
end