How to make model associations between two models in Ruby. Or How to take data from one model and use it in another model?

Question

So I create two models, one "Course" and one "Section" with scaffold and need Section to display Courses in a drop down menu that reflects any courses that were created in the course model and use it to create in section. I've been able to get the drop down menu displaying the courses created from "Course", but when I create the new section is displays the course as blank. Course has a Name, Department, Number, and Credit Hours. Section has Semester, Number, Course, and Room Number.

What I modified to make the drop down menu was ( in _form.html.erb of views of section )

  <div class="field">
  <%= form.label "Courses", class: 'courses'%>
  <%= form.collection_select(:section, Course.all, :id, :name) %>
  </div>

This gives an error of "Courses must exist"

Previously I had:

  <div class="field">
  <%= form.label "Courses", class: 'courses'%>
  <%= form.collection_select(:course_ids, Course.all, :id, :name) %>

This did not give an error and allowed me to create a section, just without adding the selected course to the section database.

https://api.rubyonrails.org/classes/ActionView/Helpers/FormOptionsHelper.html#method-i-collection_select

From reading it appears :name should be defined in the models portion of Course, but when I try it gives an error. I also realize I do not have it set to record Course to a specific section ID which is why it isn't saving it when a new section is created. My question is, what do I add or modify to make that work? Is using collection select the wrong thing to do?

EDIT to include sections_controller.rb

class SectionsController < ApplicationController
  before_action :set_section, only: [:show, :edit, :update, :destroy]

  # GET /sections
  # GET /sections.json
  def index
    @sections = Section.all
  end

  # GET /sections/1
  # GET /sections/1.json
  def show
  end

  # GET /sections/new
  def new
    @section = Section.new
  end

  # GET /sections/1/edit
  def edit
  end

  # POST /sections
  # POST /sections.json
  def create
    @section = Section.new(section_params)

    respond_to do |format|
      if @section.save
        format.html { redirect_to @section, notice: 'Section was successfully created.' }
        format.json { render :show, status: :created, location: @section }
      else
        format.html { render :new }
        format.json { render json: @section.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /sections/1
  # PATCH/PUT /sections/1.json
  def update
    respond_to do |format|
      if @section.update(section_params)
        format.html { redirect_to @section, notice: 'Section was successfully updated.' }
        format.json { render :show, status: :ok, location: @section }
      else
        format.html { render :edit }
        format.json { render json: @section.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /sections/1
  # DELETE /sections/1.json
  def destroy
    @section.destroy
    respond_to do |format|
      format.html { redirect_to sections_url, notice: 'Section was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_section
      @section = Section.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def section_params
      params.require(:section).permit(:semester, :number, :course, :room_number)
    end
end

I believe I need to relate them somehow with the last part:

 def section_params
          params.require(:section).permit(:semester, :number, :course, :room_number)

EDIT:
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http://rubyisonrails.com/pictures/part2.PNG">

Update your question with the model associations between the two models. — Pavan, Sep 23 '18 at 18:57
Thank you, sorry I'm brand new to Ruby, Done examples out of the book and now trying to do something without a step by step and just got stuck on this part — anybodii, Sep 23 '18 at 19:11
Sections just needs to read what courses have been created using the course model. So for instance, Course model creates a course called Math 101, Science 102, and Art 103.. Section model needs to be able to display a drop down menu that shows the courses that were created such as Math 101, Science 102, and Art 103. If new courses are created later, then these would automatically show up ( in the drop down menu ) if a new Section were to be created or an old section were to be edited. I hope that makes sense. — anybodii, Sep 23 '18 at 19:45
Just tell me do you have associations between those two models or not? Or just post the models code. — Pavan, Sep 23 '18 at 19:47
class Course < ApplicationRecord has_many :sections end class Section < ApplicationRecord belongs_to :courses end — anybodii, Sep 23 '18 at 19:59

Pavan · Accepted Answer · 2018-09-23T20:20:29.900

First, you should change courses to course in the Section model. The association name for the belongs_to should always be singular

class Section < ApplicationRecord
  belongs_to :course #singular name
end

Second, you should have course_id column instead of course in the sections table. You can generate a migration which will reflect these changes in the table

rails g migration modify_sections

The above command should generate a file like xxxxxxxmodify_sections.rb under db/migrate folder. Open the file and add

def change
  add_column :sections, :course_id, :integer
  remove_column :sections, :course, :integer
end

and do rake db:migrate

Now change the collection_select like the below

<%= form.collection_select(:course_id, Course.all, :id, :name) %>

And in the sections_controller#create, add

@section.course_id = params[:section][:course_id]

before the respond_to do |format|

Finally, change course to course_id in the section_params method.

def section_params
  params.require(:section).permit(:semester, :number, :course_id, :room_number)
end

Note:

As you are very new to the technology, I recommend you to follow the Guides to learn.

Thank you. That made it work, but when I saved it, instead of saving it the course name such as "Course 2" it saved it as "" Do you know what would cause this? — anybodii, Sep 23 '18 at 20:45
@anybodii Can you update the question with the params that apppear in the server log when you click on submit? — Pavan, Sep 24 '18 at 06:02
http://rubyisonrails.com/pictures/part1.PNG http://rubyisonrails.com/pictures/part2.PNG — anybodii, Sep 27 '18 at 05:45

How to make model associations between two models in Ruby. Or How to take data from one model and use it in another model?

1 Answers1