用Rails设计模型

Question

我有以下几种型号：

• 研究所
• 学生
• 教室
• 课程

Requirements:

1. 一个教室可以有许多课程。一门课程可以属于许多教室。
2. 一个教室可以有许多学生。一个学生可以属于许多教室。
3. 一个学生可以选修许多课程。一门课程可以属于许多学生。
4. 一个学院有许多学生，许多教室和许多课程。

我试图为上面的内容创建关联:下面的内容是否准确？

1. 学院： has_and_belongs_to_many :学生会has_many :教室has_many :课程
2. 学生： has_and_belongs_to_many :研究所
3. 教室： has_and_belongs_to_many :学生
4. 课程： has_and_belongs_to_many :学生会has_many :教室belongs_to :研究所

我怎么才能在这里使用“贯穿”关系呢？

Answer 1

对Classroom关联和Cource关联做类似的操作

跑：

ruby homework.rb

#homework.rb
require 'active_record'

`rm foobar.db`

class User < ActiveRecord::Base
  establish_connection adapter: 'sqlite3', database: 'foobar.db'
  connection.create_table table_name, force: true do |t|
    t.string :name
  end
  connection.create_table :institutes_users, id: false do |t|
    t.integer :user_id
    t.integer :institute_id
  end

  has_and_belongs_to_many :institutes
end

class Institute < ActiveRecord::Base
  establish_connection adapter: 'sqlite3', database: 'foobar.db'
  connection.create_table table_name, force: true do |t|
    t.string :name
  end
  connection.create_table :institutes_students, id: false do |t|
    t.integer :student_id
    t.integer :institute_id
  end

  has_and_belongs_to_many :users
  has_and_belongs_to_many :students
  has_many :classrooms
  has_many :courses
end

class Student < ActiveRecord::Base
  establish_connection adapter: 'sqlite3', database: 'foobar.db'
  connection.create_table table_name, force: true do |t|
    t.string :name
  end
  connection.create_table :classrooms_students, id: false do |t|
    t.integer :student_id
    t.integer :classroom_id
  end

  has_and_belongs_to_many :institutes
  has_and_belongs_to_many :classrooms
  has_many :courses
end

class Classroom < ActiveRecord::Base
  establish_connection adapter: 'sqlite3', database: 'foobar.db'
  connection.create_table table_name, force: true do |t|
    t.string :name
    t.references :institute
  end

  belongs_to :institute
  has_and_belongs_to_many :students
end

class Course < ActiveRecord::Base
  establish_connection adapter: 'sqlite3', database: 'foobar.db'
  connection.create_table table_name, force: true do |t|
    t.string :name
    t.references :institute
    t.references :student
  end

  belongs_to :institute
  belongs_to :student
end
user = User.create!(name: 'John')
institute = Institute.create!(name: 'Harvard')
student = Student.create(name: 'Mary')
institute.users << user
institute.classrooms.create(name: '4th floor room')
institute.courses.create(name: 'IT')
institute.students << student
student.classrooms << Classroom.create(name: '5th froor room')
student.courses << Course.create(name: 'Biology')
p institute.users
p institute.classrooms
p institute.courses
p institute.students
p student.classrooms
p student.courses