Songs and Tags

gistfile1.rb

# Models 

class Song < ActiveRecord::Base
  has_many :song_tags
  has_many :tags, :through => :song_tags
end
class SongTag < ActiveRecord::Base
  belongs_to :song
  belongs_to :tag
end
class Tag < ActiveRecord::Base
  has_many :song_tags
  has_many :songs, :through => :song_tags
end


# Migrations

class CreateSongs < ActiveRecord::Migration
  def change
    create_table :songs do |t|
      t.string :name
      t.string :genre

      t.timestamps
    end
  end
end
class CreateTags < ActiveRecord::Migration
  def change
    create_table :tags do |t|
      t.string :name

      t.timestamps
    end
  end
end
class CreateSongTags < ActiveRecord::Migration
  def change
    create_table :song_tags do |t|
      t.integer :song_id
      t.integer :tag_id

      t.timestamps
    end
  end
end

# Usage

1.9.2-p290 :001 > song = Song.create(name: "Let them bitches dance (remix)")
  SQL (61.4ms)  INSERT INTO "songs" ("created_at", "genre", "name", "updated_at") VALUES (?, ?, ?, ?)  [["created_at", Tue, 03 Jan 2012 13:37:12 UTC +00:00], ["genre", nil], ["name", "Let them bitches dance (remix)"], ["updated_at", Tue, 03 Jan 2012 13:37:12 UTC +00:00]]
 => #<Song id: 8, name: "Let them bitches dance (remix)", genre: nil, created_at: "2012-01-03 13:37:12", updated_at: "2012-01-03 13:37:12"> 
1.9.2-p290 :002 > tag = Tag.create(name: "Awesum!!!")
  SQL (2.3ms)  INSERT INTO "tags" ("created_at", "name", "updated_at") VALUES (?, ?, ?)  [["created_at", Tue, 03 Jan 2012 13:37:24 UTC +00:00], ["name", "Awesum!!!"], ["updated_at", Tue, 03 Jan 2012 13:37:24 UTC +00:00]]
 => #<Tag id: 11, name: "Awesum!!!", created_at: "2012-01-03 13:37:24", updated_at: "2012-01-03 13:37:24"> 
1.9.2-p290 :003 > song.song_tags.create(:tag_id => tag.id)
  SQL (1.6ms)  INSERT INTO "song_tags" ("created_at", "song_id", "tag_id", "updated_at") VALUES (?, ?, ?, ?)  [["created_at", Tue, 03 Jan 2012 13:37:36 UTC +00:00], ["song_id", 8], ["tag_id", 11], ["updated_at", Tue, 03 Jan 2012 13:37:36 UTC +00:00]]
 => #<SongTag id: 9, song_id: 8, tag_id: 11, created_at: "2012-01-03 13:37:36", updated_at: "2012-01-03 13:37:36"> 
1.9.2-p290 :004 > song.tags.all
  Tag Load (0.7ms)  SELECT "tags".* FROM "tags" INNER JOIN "song_tags" ON "tags"."id" = "song_tags"."tag_id" WHERE "song_tags"."song_id" = 8
 => [#<Tag id: 11, name: "Awesum!!!", created_at: "2012-01-03 13:37:24", updated_at: "2012-01-03 13:37:24">]