# in db/migrate

class CreateArticlesTags < ActiveRecord::Migration
  def self.up
    create_table :articles_tags do |t|
      t.integer :article_id
      t.integer :tag_id
    end
    
  end

  def self.down
    drop_table :articles_tags
  end
end

# in app/models/article.rb
class Article < ActiveRecord::Base
  has_and_belongs_to_many :tags
end

# in app/models/tag.rb
class Tag < ActiveRecord::Base
  has_and_belongs_to_many :articles
end