Active Record Associations to prevent duplicate database entries - ruby-on-rails

Question

I am setting up a Ruby on Rails application where a User will have an Album collection. My initial thinking was to set it up with a simple User has_many Albums and Albums belongs to Users. The problem that arises here is that the Album table will have duplicates entries, only distinguished by user_id.
id | album_name | artist_id | created_at | updated_at | user_id
-----+-------------+-----------+----------------------------+----------------------------+---------
2 | SuperRando | 3 | 2015-11-13 00:03:51.790759 | 2015-11-13 00:03:51.790759 | 1
3 | SuperRando | 3 | 2015-11-13 00:19:08.438907 | 2015-11-13 00:19:08.438907 | 2
So what would be the best course of action so I could have an Album table with all unique albums?

Answer 1

You could model it using a join table:
class Album < ActiveRecord::Base
has_many :user_albums
has_many :users, through: :user_albums
end
class User < ActiveRecord::Base
has_many :user_albums
has_many :albums, through: :user_albums
end
class UserAlbum < ActiveRecord::Base
belongs_to :user
belongs_to :album
end
So, your schema would like somewhat like this:
create_table "albums", force: :cascade do |t|
t.string "name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "user_albums", force: :cascade do |t|
t.integer "user_id"
t.integer "album_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "users", force: :cascade do |t|
t.string "email"
t.string "first_name"
t.string "last_name"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
Now, the way you would call this code in your controller or console. you can do this:
Create User: user = User.create(params)
Find or Create an album: album = Album.find_or_create_by(params)
Associate user with that album user.albums << album & then save it by user.save
Now to see user's album. you can do:
User.take.albums
to see users of a particular album, you can do
Album.take.users
Hope this answers your question.
For more information have a look at the rails guides:
http://guides.rubyonrails.org/association_basics.html#the-has-many-through-association