HABTM关联下拉列表选择

Question

I am trying to create a dropdown select on a form. I have a HABTM association between professors and classrooms:

Classroom Model:

class Classroom < ApplicationRecord
  has_and_belongs_to_many :professors
end

Professor Model:

class Professor < ApplicationRecord
  has_and_belongs_to_many :classrooms
end

Strong Params:

def classroom_params
  params.require(:classroom).permit(:name, :professor_ids => [])
end

I am trying to find a way to use f.select instead of select_tag inside the form. But when I do it, the database does not save the values. This way works:

<%= form_for @classroom do |f| %>
  <%= f.label :name %><br>
  <%= f.text_field :name %><br>
  <% array = Professor.all.map { |professor| [professor.user.name, professor.id] } %>
  <%= select_tag "classroom[professor_ids][]", options_for_select(array) %>
<% end %>

But I am trying like that and it is not working:

<%= form_for @classroom do |f| %>
  <%= f.label :name %><br>
  <%= f.text_field :name %><br>
  <% array = Professor.all.map { |professor| [professor.user.name, professor.id] } %>
  <%= f.select :professor_ids, options_for_select(array) %>
<% end %>

The view works correctly but when I submit the form, the value doesn't go to to the classroom_params. I tried to debug it stopping the controller after the submit and I got this:

The params came correctly with all the information submitted, but the classroom_params came missing the professor_ids. Is there a way to do this dropdown using f.select ?

Answer 1

You whitelisted the array of 'professor_ids', but your 'select' input returns 1 string ( "prefessor_ids" => "2" from you screenshot). Maybe you want to set the select as 'multiple'? (I have not tested it, but i think params will be whitelisted correctly after that)

<%= form_for @classroom do |f| %>
  <%= f.label :name %><br>
  <%= f.text_field :name %><br>
  <%= s.collection_select :professor_ids, Professor.all, :id, :name, multiple: true  %>
<% end %>

where

class Professor
  ...
  delegate :name, to: :user
end

Update

You probably don't have 'cfg' variable in your controller action.