how to write this query of many-to-many base in rails - ruby-on-rails

Question

Hey guys
I'm new to rails, There's a lot of eye-opener for me, and I write some code and it seems no efficient, I paste my code below, could you help me find a better way to write this.
videos table:
class CreateVideos < ActiveRecord::Migration
def self.up
create_table :videos do |t|
t.string :title
t.string :desc
t.string :tudou
t.string :otherurl
t.timestamps
end
end
def self.down
drop_table :videos
end
end
drummers table:
class CreateDrummers < ActiveRecord::Migration
def self.up
create_table :drummers do |t|
t.string :first_name
t.string :middle_name
t.string :last_name
t.string :nick_name
t.boolean :gender
t.timestamps
end
end
def self.down
drop_table :drummers
end
end
and I set them to simple many-to-many association
class CreateDrummersVideosJoin < ActiveRecord::Migration
def self.up
create_table :drummers_videos, :id => false do |t|
t.integer "drummer_id"
t.integer "video_id"
end
end
def self.down
drop_table :drummers_videos
end
end
I want to find all the title of drummer first name is "Jojo" last name is "Mayer"'s video
my code:
title = Drummer.where(:first_name => "Jojo", :last_name => "Mayer").first.videos.each {|t| t.title}
This return all the column's data, not the only the title I want
and since the there's only one result return named "Jojo Mayer", But the return value is activeRelation, I can't call videos, so my work around is using :first to get the video instance in order to call the videos. I know it's definitely not the way doing it
any suggestion?

Answer 1

You need a join table in between them like you infer. But that join table in Rails does not have to be created in a migration. It can be done exclusively in the models.
#drummer.rb
belongs_to :drummer_videos, :polymorphic => true
has_many :videos, :as => :drummer_videos
#video.rb
belongs_to :drummer_videos, :polymorphic => true
has_many :drummers, :as => :drummer_videos
Make sure that the drummer TABLE and video TABLE have a drummer_videos_id attribute.
Then you can call your Drummer..
Drummer.where(:first_name => "Jojo", :last_name => "Mayer").videos.each {|t| t.title}

Answer 2

First off, if you want to get only the title attribute from the videos you should use map or collect instead of each, so something like this:
Drummer.where(...).first.videos.map{ |t| t.title }
or even shorter:
.map(&:title)
Second, it seems to me that if you really want to get all the videos from a single Drummer object, than using first in some way or another, like you do, is a pretty good option.
Otherwise, if you want to get all videos from different Drummers according to a certain criteria, then you should probably call Video directly and then join or include the Drummer. Perhaps like this:
Video.joins(:drummers).where("drummers.first_name = 'jojo' AND drummers.last_name = 'Mayer'").map(&:title)