Question

I have a Post model:

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

  belongs_to :user

  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

a Tag model:

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

and an User model:

class User < ActiveRecord::Base
  # Include default devise modules. Others available are:
  # :token_authenticatable, :encryptable, :confirmable, :lockable, :timeoutable and :omniauthable
  devise :database_authenticatable, :registerable,
         :recoverable, :rememberable, :trackable, :validatable,
         :omniauthable

  # Setup accessible (or protected) attributes for your model
  attr_accessible :email, :password, :password_confirmation, :remember_me, :username, :avatar

  has_many :posts, :dependent => :destroy
  has_many :subscriptions
  has_many :subscribed_tags, :source => :tag, :through => :subscriptions
end

posts and tags have a many-to-many relationship (the following is the model for the join table):

class Tagging < ActiveRecord::Base
  belongs_to :post  
  belongs_to :tag
end

users and tags have also a many-to-many relationship:

class Subscription < ActiveRecord::Base
  belongs_to :user  
  belongs_to :tag
end

Only posts with tags that the user has subscribed to should display:

  def index
    @title = "Posts"
    @posts = current_user.subscribed_tags.map(&:posts).flatten.paginate(:page => params[:page], :per_page => 5)

Let say I create a tag for a post:

$ post.tags.create(:name => "food")
$ post.tags
=> [#<Tag id: 6, name: "food", created_at: "2012-03-02 10:03:59", updated_at: "2012-03-02 10:03:59"] 

Now I have no idea how to subscribe the user to that tag.

I tried this:

$ user.subscribed_tags.create(:name => "food")
$ post.tags
=> [#<Tag id: 7, name: "food", created_at: "2012-03-02 10:04:38", updated_at: "2012-03-02 10:04:38"] 

But as you can see it actually creates a new tag instead of adding the food tag with ID 6 to the user.subscribed_tags attribute.

Any suggestions to solve this issue?

Answer 1

You can append to the user’s subscriped_tags, as you would do an array.

ex: user.subscribed_tags << Tag.find_by_name("food")