Recommended way to create a joint table using ruby on rails: rails generate scaffold, rails generate model, or rails generate migration?

Question

I want to create a third table to indicated the many-to-many relation between table A and table B. Say table A corresponds to a Course model and table B correspond to a Subject table. Which of the following way do you recommend to generate the third joint table:

1. rails generate scaffold Course_subject course_id:integer subject_id:integer
2. rails generate model course_subject
3. rails generate migration course_subject understanding

My understanding is that using option 1 will generate the controller, model and view; option 2 doesn't generate the controller so if I want to see the result on website I will need to create the view file by hand; options 3 simply generates a migration file, nothing else. Am I getting this correctly? And is option 1 more convenient or not necessary?

Answer 1

Yes, you are doing it correctly. They are all correct as long as it serves its purpose. It boils down to what you want to accomplish.

Option 1 will give you everything you need but that will give you unnecessary views . In rails, you still have control over your files/code. Removing a file is just a click away. Scaffolding is just a tool to help us develop apps with less effort.

If it is a basic association where you only have foreign keys, then you can use option 2. Generate a model with a migration. You can generate controller later when you need it.

Option 3 will generate a migration but will not include the CourseSubject model. You have to create it yourself. Course and Subject model should define has_many associations and CourseSubject model with belongs_to association. This will make course.subjects chaining work.

class CourseSubject
  belongs_to :course
  belongs_to :subject
end

Answer 2

Command 1 creates a resource from scratch: migration, model, routing, controller and views. It also creates tests and some assets:

$ rails g scaffold course_subject course_id:integer subject_id:integer
  invoke  active_record
  create    db/migrate/20181022020611_create_course_subjects.rb
  create    app/models/course_subject.rb
  invoke    test_unit
  create      test/models/course_subject_test.rb
  create      test/fixtures/course_subjects.yml
  invoke  resource_route
   route    resources :course_subjects
  invoke  scaffold_controller
  create    app/controllers/course_subjects_controller.rb
  invoke    erb
  create      app/views/course_subjects
  create      app/views/course_subjects/index.html.erb
  create      app/views/course_subjects/edit.html.erb
  create      app/views/course_subjects/show.html.erb
  create      app/views/course_subjects/new.html.erb
  create      app/views/course_subjects/_form.html.erb
  invoke    test_unit
  create      test/controllers/course_subjects_controller_test.rb
  create      test/system/course_subjects_test.rb
  invoke    helper
  create      app/helpers/course_subjects_helper.rb
  invoke      test_unit
  invoke    jbuilder
  create      app/views/course_subjects/index.json.jbuilder
  create      app/views/course_subjects/show.json.jbuilder
  create      app/views/course_subjects/_course_subject.json.jbuilder
  invoke  assets
  invoke    coffee
  create      app/assets/javascripts/course_subjects.coffee
  invoke    scss
  create      app/assets/stylesheets/course_subjects.scss
  invoke  scss
  create    app/assets/stylesheets/scaffolds.scss

Command 2 creates migration, model and test for model:

$ rails g model course_subject
  invoke  active_record
  create    db/migrate/20181022020655_create_course_subjects.rb
  create    app/models/course_subject.rb
  invoke    test_unit
  create      test/models/course_subject_test.rb
  create      test/fixtures/course_subjects.yml

Command 3 creates migration only:

$ rails g migration course_subject
  invoke  active_record
  create    db/migrate/20181022020717_course_subject.rb

Which option to choose depends on association you're going to use. For plain has_and_belongs_to_many association you do not need a model for a join table. Just create a migration then - command 3 is your choice. Note that the join table should follow some naming rules and in this case be named courses_subjects . Example of migration:

create_table courses_subjects, id: false do |t|
  t.references  :course
  t.references  :subject
end

(Fields id , created_at and updated_at are not created since they are not necessary here)

Otherwise, if for some reason you're going to have access to join table using model class, or for has_many ... through association, you will need to create a model as well. So use command 2 then.