Help us understand the problem. What is going on with this article?

Rails4で中間テーブルがポリモーフィックなテーブルとhas_many throughする

More than 5 years have passed since last update.

問題

中間テーブルを簡単につなぐことができるhas_many throughは便利だけど、中間テーブルがポリモーフィックな場合はどう書けばいいの?

こう書けば良い

以下の図のように、StudyPaticipantが中間テーブルかつポリモーフィックなモデルだとします。

  User - has_many -> StudyParticipant - has_many -> Subsciption
                                      - has_many -> Adoption

で、こんな感じにSubscriptionやAdoptionを引っ張りたい。

user.subscriptions
user.adoptions

そんなときはこんな感じに定義すれば良いようです。

# user.rb
class User < ActiveRecord::Base
  has_many :study_participants
  has_many :subscriptions, through: :study_participants, source: :study, source_type: 'Subscription'
  has_many :adoptions, through: :study_participants, source: :study, source_type: 'Adoption'
end

# study_participant.rb
class StudyParticipant < ActiveRecord::Base
  belongs_to :study, polymorphic: true
end

# subscription.rb
class Subscription < ActiveRecord::Base
  has_many :study_participants, as: :study
end

# adoption.rb
class Adoption < ActiveRecord::Base
  has_many :study_participants, as: :study
end

Rails3のときはhas_manyのconditionsキーでベタに書いていた気がするのですが、Rails4からはsource_typeというキーが用意されていました。

Why not register and get more from Qiita?
  1. We will deliver articles that match you
    By following users and tags, you can catch up information on technical fields that you are interested in as a whole
  2. you can read useful information later efficiently
    By "stocking" the articles you like, you can search right away
Comments
No comments
Sign up for free and join this conversation.
If you already have a Qiita account
Why do not you register as a user and use Qiita more conveniently?
You need to log in to use this function. Qiita can be used more conveniently after logging in.
You seem to be reading articles frequently this month. Qiita can be used more conveniently after logging in.
  1. We will deliver articles that match you
    By following users and tags, you can catch up information on technical fields that you are interested in as a whole
  2. you can read useful information later efficiently
    By "stocking" the articles you like, you can search right away
ユーザーは見つかりませんでした