gistfile1.txt

class Client
  include Mongoid::Document
  field :name
  field :description
  field :version

  references_many :contents
end

class Content
  include Mongoid::Document
  field :key
  field :value

  referenced_in :client
end

client = Client.create!(:name => 'border', :description => 'lala')    
content = Content.create!(:key => 'help_about', :value => 'hello there')
client.content = content