Mongoid_tags

mongoid_tags.rb

class Tag
  include Mongoid::Document
  field :name
  embedded_in :taggable, polymorphic: true
end

class Category
  include Mongoid::Document
  embeds_many :tags, class_name: "Tag", as: :taggable
  def tag_list
    tags.map(&:name).join(",")
  end
  def tag_list=(s)
    tags.clear
    s.split(",").map(&:strip).each { |n| tags.new(name: n) }
  end
end

# c = Category.create
# c.update_attributes :tag_list => "a"
# c.reload
# c.tag_list # => "a"

# c.update_attributes :tag_list => "a,b"
# c.reload
# c.tag_list # => "a,a,b" :(