如何仅在联接表导轨中添加记录

Question

I have model Program , Courses and Student . There is many_to_many relationship between program course and student course ...

So first i add program's courses then i show program courses to student so that he can take courses but problem is that whenever i create student courses it adds course in course table too i just want to add course_id and student_id in join table and don't want to add course in course table because courses are already there..

my course controller

def create
  @program = Program.find(params[:program_id]) if params[:program_id]
  @course = @program.courses.create(program_course_params) if @program
  @student = Student.find(params[:student_id]) if params[:student_id]
  if params[:student_id]
    params[:student].each do |cid|
      @course = @student.courses.create(name:cid) if @student
    end
  end
end

Form

 <table>
    <% @student.program.courses.each do |c| %>
    <tr><td><%=c.name %><td> 
    <td><%= check_box_tag "student[]",c.name,:name %></td>
    </tr>
    <% end %>
    <tr>
   </table>

class Course < ActiveRecord::Base
    has_and_belongs_to_many :students
    has_and_belongs_to_many  :programs

end

class Program < ActiveRecord::Base
    has_and_belongs_to_many :courses
    has_many :students
end

class Student < ActiveRecord::Base
    has_and_belongs_to_many :courses

    belongs_to :program
end

Answer 1

Try the following code.

def create
  @program = Program.find(params[:program_id]) if params[:program_id]
  @course = @program.courses.create(program_course_params) if @program
  @student = Student.find(params[:student_id]) if params[:student_id]
  if params[:student_id]
    params[:student].each do |cid|
      course_to_add = Course.find_by_id(cid)
      @course = @student.courses << course_to_add unless course_to_add.blank?
    end
  end
end

Answer 2

this line is telling rails to create an entirely new course, and associate that course to the student

@course = @student.courses.create(name:cid) if @student

i believe you mean to shovel the course onto the students array of courses like this:

@student.courses << course

or maybe, since it appears your students_courses table also includes a name attribute rather than simply having id's of the joined objects, you may need to do this

StudentsCourse.create( student: @student, course: @course, name: cid)

there may be some errors in the above code, but without seeing more of your source code it is hard to tell from the way the question is presented whether i have the name of the join table correct. this will also require a model for the join table, if you don't already have that.

Answer 3

Your current code is highly inefficient, you'll be better using the collection_singular_ids method if you want to just populate the join:

#config/routes.rb
resources :programs do
  resources :students do
    match :courses, via: [:get, :put] #-> url.com/programs/:program_id/students/:student_id/courses
  end

#app/controllers/students_controller.rb
class StudentsController < ApplicationController 
   def courses
     @program = Program.find params[:program_id]
     @student = Student.find params[:student_id]
     @courses = Course.all
     @student.update course_id_params if request.put?
   end

   private

   def course_id_params
     params.require(:student).permit(course_ids: [])
   end
end

#app/views/students/courses.html.erb
<%= form_for @student do |f| %>
   <%= f.collection_check_boxes :course_ids, @courses, :id, :name %>
   <%= f.submit %>
<% end %>