Question

I have a Sezzion model:

attr_accessible  :description
has_many :session_instructors, :dependent => :destroy
has_many :instructors, :through => :session_instructors
accepts_nested_attributes_for :session_instructors
accepts_nested_attributes_for :instructors

Instructor model:

attr_accessible :bio
has_many :sezzions, :through => :session_instructors
has_many :session_instructors, :dependent => :destroy

SessionInstructor model:

attr_accessible :instructor_id, :sezzion_id
belongs_to :sezzion
belongs_to :instructor

Lastly, User model:

has_many :sezzions
has_many :instructors

I’m trying to create a form for Sezzion with nested form for SessionInstructor which has multiple select option for Instructors.

How can I do the following:

1. nested form for SessionInstructor
2. use multiple select option to get all the selected Instructor‘s instructor_id
3. hidden field to pass in the created/updated session_id with each select instructor

I have the following code as of now:

<%= form_for(@sezzion) do |f| %>

    <%= f.label :description %>
    <%= f.text_area :description %>


    <%= f.label :instructors %>
    <%= fields_for :session_instructors do |f| %>
      <select multiple>
        <% current_user.instructors.each do |instructor| %>
          <option><%= instructor.name %></option>
        <% end %>
      </select>
    <% end %>

    <%= f.submit %>

<% end %>

Thank you so much!

Answer 1

This is something that seems ridiculously hard in Rails.

I think something like this might work:

<%= f.fields_for :session_instructors do |si| %>
  <%= si.collection_select :instructor_ids, current_user.instructors, :id, :name, multiple: true>
<% end %>

This should create a form element which will set sezzion[session_instructors_attributes][instructor_ids].

Although I’m not sure if that’s actually what you want. I’ve never tried this using a multi select. If it doesn’t work, you could also try getting rid of the fields_for and just using f.collection_select. If you’re willing to use a checkbox, I can show you how to do that for sure.

I hope that helps.

Edit:

Here’s how I would usually do it with a check_box:

<%= f.fields_for :session_instructors do |si| %>
  <%= si.hidden_field "instructor_ids[]" %>
  <% current_user.instructors.each do |i| %>
    <%= si.check_box "instructor_ids[]", i.id, i.sezzions.include?(@sezzion), id: "instructor_ids_#{i.id}" %>
    <%= label_tag "instructor_ids_#{i.id}", i.name %>
  <% end %>
<% end%>

There are a couple “gotchas!” with this method. When editing a model, if you deselect all checkboxes then it won’t send the parameter at all. That’s why the hidden_field is necessary. Also, you need to make sure each form element has a unique id field. Otherwise only the last entry is sent. That’s why I manually set the value myself.

I copy pasted and then edited. Hopefully I got the syntax close enough where you can get it to work.

FINAL EDIT:

Per Sayanee’s comment below, the answer was a bit simpler than I thought:

<%= f.collection_select :instructor_ids, current_user.instructors, :id, :name, {}, {:multiple => true} %>