如何编写 Rails SQL 查询以查找所有子对象具有相同值的对象

Question

我一直在阅读这篇文章，但无法将其写入 Rails 范围：

find all parent records where all child records have a given value (but not just some child records)

我有一个 Course、Section 和 Quiz 对象：

class Course < ActiveRecord::Base
  has_many :course_members
  has_many :members, through: :course_members
  has_many :sections
  has_many :quizzes, through: :sections
end

class Quiz < ActiveRecord::Base
  belongs_to :member
  belongs_to :section
end

class Section < ActiveRecord::Base
  belongs_to :course
  has_many :quizzes
end

我想查找会员的所有课程，其中与该课程相关的所有测验都具有completed = true 属性。

所以在我的Member 课程中，我最好写一些类似的东西：

has_many :completed_courses, -> { 
   joins(:courses, :quizzes, :sections)
   # .select( 'CASE WHEN quizzes.completed = true then 1 end') ??? maybe ???
}, class_name: 'Course'

哈哈！但除非这太复杂了。我一直在尝试把这个简单地写在Course 中也可以。

Answer 1

class Member < ActiveRecord::Base
  has_many :courses, through: :course_members
  has_many :course_members

  has_many :completed_courses,
    -> { joins(:quizzes).where.not(quizzes: {completed: [false, nil]}) },
    through: :course_members,
    source: :course
end

如果您的 completed 布尔列是 NOT NULL，则将上面的 [false, nil] 更改为简单的 false

使用示例

irb(main):002:0> Member.first.completed_courses
  Member Load (0.2ms)  SELECT "members".* FROM "members" ORDER BY "members"."id" ASC LIMIT 1
  Course Load (0.1ms)  SELECT "courses".* FROM "courses" INNER JOIN "sections" ON "sections"."course_id" = "courses"."id" INNER JOIN "quizzes" ON "quizzes"."section_id" = "sections"."id" INNER JOIN "course_members" ON "courses"."id" = "course_members"."course_id" WHERE (NOT (("quizzes"."completed" = 'f' OR "quizzes"."completed" IS NULL))) AND "course_members"."member_id" = ?  [["member_id", 1]]