tracks/app/models/tag.rb

# The Tag model. This model is automatically generated and added to your app if
# you run the tagging generator included with has_many_polymorphs.

class Tag < ActiveRecord::Base

  DELIMITER = "," # Controls how to split and join tagnames from strings. You may need to change the <tt>validates_format_of parameters</tt> if you change this.
  JOIN_DELIMITER = ", "

  # If database speed becomes an issue, you could remove these validations and
  # rescue the ActiveRecord database constraint errors instead.
  validates_presence_of :name
  validates_uniqueness_of :name, :case_sensitive => false

  # Change this validation if you need more complex tag names.
  # validates_format_of :name, :with => /^[a-zA-Z0-9\_\-]+$/, :message => "can not contain special characters"

  # Set up the polymorphic relationship.
  has_many_polymorphs :taggables,
    :from => [:todos, :recurring_todos],
    :through => :taggings,
    :dependent => :destroy,
    :skip_duplicates => false,
    :parent_extend => proc {
    # Defined on the taggable models, not on Tag itself. Return the tagnames
    # associated with this record as a string.
    def to_s
      self.map(&:name).sort.join(Tag::JOIN_DELIMITER)
    end
    def all_except_starred
      self.reject{|tag| tag.name == Todo::STARRED_TAG_NAME}
    end
  }

  # Callback to strip extra spaces from the tagname before saving it. If you
  # allow tags to be renamed later, you might want to use the
  # <tt>before_save</tt> callback instead.
  def before_create
    self.name = name.downcase.strip.squeeze(" ")
  end

  def on(taggable, user)
    taggings.create :taggable => taggable, :user => user
  end

  # Tag::Error class. Raised by ActiveRecord::Base::TaggingExtensions if
  # something goes wrong.
  class Error < StandardError
  end

end