Rails:引用独立实体

# app/models/user.rb
class User < ApplicationRecord
  has_one :profile
end

# app/models/profile.rb
class Profile < ApplicationRecord
  belongs_to :user
end

# app/models/user.rb
class User < ApplicationRecord
  has_many :posts
end

# app/models/post.rb
class Post < ApplicationRecord
  belongs_to :user
end

# app/models/student.rb
class Student < ApplicationRecord
  has_and_belongs_to_many :courses
end

# app/models/course.rb
class Course < ApplicationRecord
  has_and_belongs_to_many :students
end

# db/migrate/XXXXXX_create_courses_students.rb
class CreateCoursesStudents < ActiveRecord::Migration[6.1]
  def change
    create_join_table :courses, :students do |t|
      # t.index [:course_id, :student_id]
      # t.index [:student_id, :course_id]
    end
  end
end

# 获取用户的所有帖子
user = User.find(1)
user.posts # => #<ActiveRecord::Associations::CollectionProxy [#<Post id: 1, user_id: 1, title: "First Post">]>

# 获取帖子的用户
post = Post.find(1)
post.user # => #<User id: 1, name: "John Doe">

# 获取学生的所有课程
student = Student.find(1)
student.courses # => #<ActiveRecord::Associations::CollectionProxy [#<Course id: 1, name: "Math">]>

# 获取课程的所有学生
course = Course.find(1)
course.students # => #<ActiveRecord::Associations::CollectionProxy [#<Student id: 1, name: "Alice">]>