Passing id to form_with in rails

Question

For a university group project we are creating a rails application where Uni courses can be created, accessed etc.

One of the requirements for the project "A Course Coordinator must be able to set a user as a marker for a given course". To solve this, there is a Role Table which stores user_id, course_id, and the role, in this case "Marker".

I have created a view where the Course Coordinator can select a user from all Users and Set them as a Marker. This occurs on the courses/assign_marker page. The controller method for this page is shown below:

def assign_marker
    @users = User.enrolled_users
    @course = Course.find(params[:id])
end

Here, enrolled_users just returns all users which aren't admins (this works), and params[:id] is the course_id. If I use puts I can see that it has the correct value, so that's all working.

My problem occurs in my function to handle the post request:

def add_marker

    Role.assign_marker(params[:user_id], params[:id])           

    # Flash
    flash[:notice] = "#{User.find(params[:user_id]).username} was assigned as Marker to #{Course.find(params[:id]).courseName}"

    # Refresh
    redirect_back(fallback_location: root_path)

end

Upon submitting my form, I find that add_marker sees params[:id] as blank. Below is my form in haml (which corresponds to the assign_marker function)

= form_with url: 'assign_marker', :id => "#{@course.id}" do |f|
  .row
    .input-field

      -# Display username in selection & store id as parameter
      = f.collection_select(:user_id, @users, :id, :username, :include_blank => true)

      %label Users

 = button_tag "Set as Marker", {:class => "waves-effect waves-light btn"} 

If I place #{@course.id} anywhere within the view I can see the correct course_id displayed. I attempted to set the id in the form_with as shown above, since that is what I'd do with form_tag. Clearly that isn't working, and add_marker isn't seeing it through params[:id].

Also, my routes for the above get and post requests are as follows:

get 'courses/assign_marker', :to => 'courses#assign_marker'
post 'courses/assign_marker', :to => 'courses#add_marker'

I'm fairly new to rails so I'm probably missing something pretty obvious. Any help would be much appreciated :). Thank you

Answer 1

The reason :id => "#{@course.id}" is not working is because that's just used to set the HTML id property, you can see more about that here

Best solution is to use a nested route. Assuming you have resources :courses somewhere on config/routes.rb you should declare like this:

resources :courses do
  member do
    get :assign_marker
    post :add_marker
  end
end

That will generate the following routes:

GET  /courses/:id/assign_marker
POST /courses/:id/add_marker

You can then reference their paths like this:

assign_market_course(@course)
add_market_course(@course)

The other solution, which may sound simpler but it's not really the "Rails way" is to add the id as a hidden field, something like this:

= f.hidden_field :id, value: @course.id