Question

I have a Tag model with only one attribute: :name.

tag.rb:

class Tag < ActiveRecord::Base
  has_many :taggings, :dependent => :destroy  
  has_many :posts, :through => :taggings
  has_many :subscriptions
  has_many :subscribed_users, :source => :user, :through => :subscriptions
end

(it has a many-to-many relationship with a Post model):

class Post < ActiveRecord::Base
  attr_accessible :title, :content, :tag_names

  validates :title,   :presence => true,
                      :length   => { :maximum => 30 },
                      :uniqueness => true
  validates :content, :presence => true,
                      :uniqueness => true

  has_many :taggings, :dependent => :destroy
  has_many :tags, :through => :taggings

  attr_writer :tag_names
  after_save :assign_tags

  def tag_names
    @tag_names || tags.map(&:name).join(' ')
  end

  private

  def assign_tags
    if @tag_names
      self.tags = @tag_names.split(" ").map do |name|
        Tag.find_or_create_by_name(name)
      end
    end
  end
end

As you can imagine I don’t want to have 2 tags with the same name. Right now, it is possible to create them. If there is a tag like this: <Tag id=1, name=food> and later another tag like this is created: <Tag id=2, name=food>. I want the second to be ignored because there is already a tag with the name food.

(Pretty much how all tag systems works)

Any suggestions in order to accomplish this?

Answer 1

I am not sure if I completely understand your problem but maybe this will be helpful for you.
…

private

def assign_tags
  return if @tag_names.blank?
  @tag_names.split(" ").each do |name|
    tag = Tag.find_or_create_by_name(name)
    self.tags << tag unless tags.include?(tag)
  end
end