class Period
  include MongoMapper::EmbeddedDocument

  key :text, String

  embedded_in :schedule

  def to_s
    text
  end

end

class Schedule
  include MongoMapper::Document

  key :name, String

  many :periods

  def to_s
    text = "#{name}, periods: " + periods.join(', ')
  end

end

s1 = Schedule.create(:name => "Thursday",
  :periods => [
    Period.new(:text => "Morning"),
    Period.new(:text => "Afternoon"),
    Period.new(:text => "Evening")
  ])
puts s1
#Thursday, periods: Morning, Afternoon, Evening

s1.periods.delete_if{|p| p.text == 'Afternoon'}
s1.save
puts s1
# Thursday, periods: Morning, Evening