From: Lake Denman <ldenman@...>
Date: 2008-08-12T05:58:40+09:00
Subject: Re: How to map this association

Hi Wenhan,
This is how I set up my association and I think it works well... I'm 
using has_many through instead of has_and_belongs_to_many. I think that 
using has_many through is now more widely accepted than it's 
predecessor.

Anyways, on to the show. Here's what we have:
Models

User:
  has_many :videos, :foreign_key=>'added_by' # in retrospect that might 
not be the best name. You could try contributor_id, maybe.
  has_many :video_collections
  has_many :collected_videos, :through=>:video_collections, 
:source=>:video # We have to specify a source since we aren't really 
following the naming convention.

Video:
  belongs_to :user, :foreign_key=>'added_by'
  has_many :video_collections
  has_many :collectors, :through=>:video_collections,:source=>:user

VideoCollection:
  belongs_to :user
  belongs_to :video


Next up, Simple Migrations for the Models!

Users
class CreateUsers < ActiveRecord::Migration
  def self.up
    create_table :users do |t|
      t.string :name

      t.timestamps
    end
    User.create!(:name=>"Lake")
  end

  def self.down
    drop_table :users
  end
end


Videos
class CreateVideos < ActiveRecord::Migration
  def self.up
    create_table :videos do |t|
      t.string :title
      t.integer :added_by

      t.timestamps
    end
    Video.create!(:title=>"Gone With The Wind", :added_by=>1)
  end

  def self.down
    drop_table :videos
  end
end


Video Collections (rumor has it that you can pass :id=>false here, but I 
forgot to do that when I generated this)
class CreateVideoCollections < ActiveRecord::Migration
  def self.up
    create_table :video_collections do |t|
      t.integer :user_id
      t.integer :video_id

      t.timestamps
    end
    VideoCollection.create!(:user_id=>1, :video_id=>1)
  end

  def self.down
    drop_table :video_collections
  end
end


Okay, so we have our migrations setup and the next thing we cna do is 
Migrate:
rake db:create:all;rake db:migrate

Then fire up the script/console in your rails_root directory: ruby 
script/console

Let's see what happens (ps. We already created some rows in the 
migrations):


#Make sure all our entities are there:
>> User.find(1)
=> #<User id: 1, name: "Lake", created_at: "2008-08-11 20:53:24", 
updated_at: "2008-08-11 20:53:24">
>> Video.find(1)
=> #<Video id: 1, title: "Gone With The Wind", added_by: 1, created_at: 
"2008-08-11 20:53:24", updated_at: "2008-08-11 20:53:24">
>> VideoCollection.find(1)
=> #<VideoCollection id: 1, user_id: 1, video_id: 1, created_at: 
"2008-08-11 20:53:24", updated_at: "2008-08-11 20:53:24">

# Check videos associated with users
>> User.find(1).videos
=> [#<Video id: 1, title: "Gone With The Wind", added_by: 1, created_at: 
"2008-08-11 20:53:24", updated_at: "2008-08-11 20:53:24">]

# Check user associated with video
>> Video.find(1).user
=> #<User id: 1, name: "Lake", created_at: "2008-08-11 20:53:24", 
updated_at: "2008-08-11 20:53:24">

# Check collected videos associated with user
>> User.find(1).collected_videos
=> [#<Video id: 1, title: "Gone With The Wind", added_by: 1, created_at: 
"2008-08-11 20:53:24", updated_at: "2008-08-11 20:53:24">]

# Check collector associated with video
>> Video.find(1).collectors
=> [#<User id: 1, name: "Lake", created_at: "2008-08-11 20:53:24", 
updated_at: "2008-08-11 20:53:24">]

# Let's make sure we really are getting different associations since 
it's only fairly proven.

# Let's create a new video
>> Video.create!(:title=>'Gone With The Wind', :added_by=>2)
=> #<Video id: 2, title: "Gone With The Wind", added_by: 2, created_at: 
"2008-08-11 20:58:43", updated_at: "2008-08-11 20:58:43">

# Let's create a new video collection for user 1 and video 2
>> VideoCollection.create(:user_id=>1, :video_id=>2)
=> #<VideoCollection id: 2, user_id: 1, video_id: 2, created_at: 
"2008-08-11 20:59:26", updated_at: "2008-08-11 20:59:26">

# Now let's ask the user for it's collected videos
>> User.find(1).collected_videos
=> [#<Video id: 1, title: "Gone With The Wind", added_by: 1, created_at: 
"2008-08-11 20:53:24", updated_at: "2008-08-11 20:53:24">, #<Video id: 
2, title: "Gone With The Wind", added_by: 2, created_at: "2008-08-11 
20:58:43", updated_at: "2008-08-11 20:58:43">]

# And now for User 1's videos that he added
>> User.find(1).videos
=> [#<Video id: 1, title: "Gone With The Wind", added_by: 1, created_at: 
"2008-08-11 20:53:24", updated_at: "2008-08-11 20:53:24">]

Hope that helps some.

Lake













Wenhan Zhou wrote:
> Hi, This is the scenario
> 
> A user can create videos and collect videos.
> 
> I was coding the creation side of the videos so I was using a belongs_to
> and a has_many.
> 
> Then when I came to the part of collecting the videos, I am stumped with
> how to implement the association.
> 
> Normally I would just use a table with user_id and video_id.
> But in this case, this would conflict with my earlier code.
> 
> so the question is this: how do I implement an association for the
> scenario belong.
> 
> A user can create multiple video that are shown on his profile page
> (1 to Many)
> user.rb :has_many :videos
> video.rb :belongs_to :user
> user table has a coloum called video_id
> 
> A user can also collect a video. This list is shown as videos favorited
> by this user(Each video can also be favourite by many people)
> (many to many)
> user.rb : has_and_belongs_to_many  :videos
> video.rb :has_and_belongs_to_many  :users
> created a new table called user_video with user_id & video_id
> 
> Since the 2 associations are for exactly the same models,
> what happens when I call @user.videos
> will I
> 1) Get the list of videos created by this user
> 2) Get the list of videos collected by this user
> 3) the system goes bonkers :(
> 
> Is this the wrong way to implement this?

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