Question

我通过Teachers为Classrooms和has_many :through建立了多对多关系设置：

class Teacher < ActiveRecord::Base
  has_many :classrooms, :through => :classroom_memberships
end

class Classroom < ActiveRecord::Base
  has_many :students
  has_many :teachers, :through => :classroom_memberships
end

class ClassroomMemberships < ActiveRecord::Base
  belongs_to :teacher
  belongs_to :classroom
end

目前，Students只能属于一个Classroom：

class Student < ActiveRecord::Base
  belongs_to :classroom
end

现在我需要跟踪学生的历史课堂会员资格，为教室创建第二个多对多关系。因此，虽然学生一次只能属于一个教室，但我需要知道去年，学生A属于教室B.

我想我有两个可行的选择：

1。）使classroom_memberships关联具有多态性，因此我会有classroomable_id和classroomable_type指向教师或学生。

2。）简化事情并将另一个外键添加到名为ClassroomMemberships的{{1}}，在这种情况下，对于给定的行，student_id或student_id将具有值。

哪个是更好的选择？

Answer 1

我可能会选择以下路线：

class Course < ActiveRecord::Base
  # like "MATH 100"
  has_many :sections
  has_many :teachers, :through => :sections
end

class Term < ActiveRecord::Base
  # like "Fall 2015"
  has_many :sections
end

class Teacher < ActiveRecord::Base
  has_many :sections
  has_many :courses, :through => :sections
end

class Section < ActiveRecord::Base
  # a course, in a term, taught by a teacher, with registered students
  belongs_to :term
  belongs_to :course
  belongs_to :teacher
  has_many :registrations
  has_many :students, :through => :registrations
end

class Registration < ActiveRecord::Base
  # a student in a specific section
  belongs_to :section
  belongs_to :student 
end

class Student < ActiveRecord::Base
  # a student's registrations are their course history
  has_many :registrations
  has_many :sections, through :registrations
end

首先，因为这是教育系统的一个相当基本的建模。

Answer 2

听起来好像你想要一个ClassroomMembershipHistory模型。

像

这样的东西

class ClassroomMembershipHistory < ActiveRecord::Base
  belongs_to :student
  belongs_to :classroom
end

使用year属性，但最容易查询您的用例。

这应该是多少：通过关系是多态的还是不是？

2 个答案: