如何在 Rails / ActiveRecord 中设置此 belongs_to 关联？

Question

我有 User 和 Review 型号。评论可以有 author 和 subject，两者都指向 User:

class Review < ApplicationRecord
  belongs_to :subject, class_name: 'User', optional: true
  belongs_to :author, class_name: 'User', optional: true
end   
class CreateReviews < ActiveRecord::Migration[5.0]
  def change
    create_table :reviews do |t|
      t.references :subject
      t.references :author
    end
  end
end

这很好用，现在我可以将两个单独的 User 对象分配给 Review 对象，以表示谁针对谁撰写了评论。

但是，用户并不知道 "know" 他作为主题或作者与多少评论相关联。我在评论中添加了 has_and_belongs_to_many :users，反之亦然，虽然可行，但并不是我想要的。

如何设置关联才能执行以下操作：

review.author = some_other_user
review.subject = user2
another_review.author = some_other_user
another_review.subject = user2

user2.a_subject_in.count
#=> 2
user2.a_subject_in
#=> [#<Review>, #<Review>]
some_other_user.an_author_in.count
#=> 2

换句话说，我如何查看 User 被保存为作者或主题的次数 belongs_to？

Answer 1

我想你正在寻找这个查询：

class User
  def referenced_in
    # this fetches you all the reviews that a user was referenced
    Review.where("reviews.author_id = :user_id OR reviews.subject_id = :user_id", user_id: id).distinct
  end
end

User.first.referenced_in #should give you all records a user was referenced

Answer 2

如果你想在用户端使用has_many关联，你需要定义两个单独的has_many关系，如

class User < ApplicationRecord
  has_many :reviews, foreign_key: :author_id
  has_many :subject_reviews, class_name: 'Review', foreign_key: :subject_id
end

现在你可以简单地使用

irb(main):033:0> s.reviews
  Review Load (0.2ms)  SELECT "reviews".* FROM "reviews" WHERE "reviews"."author_id" = ?  [["author_id", 1]]
=> #<ActiveRecord::Associations::CollectionProxy [#<Review id: 1, comment: "random", subject_id: 2, author_id: 1, created_at: "2016-07-12 01:16:23", updated_at: "2016-07-12 01:16:23">]>
irb(main):034:0> s.subject_reviews
  Review Load (0.2ms)  SELECT "reviews".* FROM "reviews" WHERE "reviews"."subject_id" = ?  [["subject_id", 1]]
=> #<ActiveRecord::Associations::CollectionProxy []>

评论：subject_reviews这个名字不好:)，改成你的要求。