Rails Nested Attributes with multiple select and strong parameters not updating

Question

My goal is to present a select form to the user, where they can select multiple options. The edit form is for a SiteGroup which is a group of an object Site.

The form should display all existing sites and highlight those which are already selected.

However the updating works, but the sites do not update.

site_group.rb

class SiteGroup < ActiveRecord::Base
   has_and_belongs_to_many :sites
   accepts_nested_attributes_for :sites
end

site_groups_controller.rb

class SiteGroupsController < ApplicationController
  before_action :set_site_group, only: [:show, :edit, :update, :destroy]

  # GET /site_groups
  # GET /site_groups.json
  def index
    @site_groups = SiteGroup.all
  end

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

  # GET /site_groups/new
  def new
    @site_group = SiteGroup.new
  end

  # GET /site_groups/1/edit
  def edit
  end

  # POST /site_groups
  # POST /site_groups.json
  def create
    @site_group = SiteGroup.new(site_group_params)

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

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

  # DELETE /site_groups/1
  # DELETE /site_groups/1.json
  def destroy
    @site_group.destroy
    respond_to do |format|
      format.html { redirect_to site_groups_url, notice: 'Site group was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_site_group
      @site_group = SiteGroup.find(params[:id])
      @sites = Site.all
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def site_group_params
      params.require(:site_group).permit(
      :name,
      :library,
      sites: [:id]
      )
    end
end

_form.html.erb for SiteGroup

<%= form_for(@site_group) do |f| %>
  <% if @site_group.errors.any? %>
    <div id="error_explanation">
      <h2><%= pluralize(@site_group.errors.count, "error") %> prohibited this site_group from being saved:</h2>

      <ul>
      <% @site_group.errors.full_messages.each do |message| %>
        <li><%= message %></li>
      <% end %>
      </ul>
    </div>
  <% end %>

  <div class="field">
    <%= f.label :name %><br>
    <%= f.text_field :name %>
  </div>
  # the @sites will also print the class, I would like to show the :name of the Site
  <%= f.select :sites,
    @sites,
    {},
    {multiple: true, size: 10}
  %>


  <div class="field">
    <%= f.label :library %>
    <%= f.text_field :library %>
  </div>
  <div class="actions">
    <%= f.submit %>
  </div>
<% end %>

How can I get the update to work and to show the name if the sites in the select field?

Answer 1

To show the names of the sites, use the collection select tag as follow:

 <%= f.fields_for :sites do |s| %>
   <%= s.collection_select :sites,
      @sites,
      :id,
      :name,
      {},
      {multiple: true, size: 10} 
   %>
 <% end %>

This is according to the documentation on collection select.

collection_select(object, method, collection, value_method, text_method, options = {}, html_options = {}) public

You can also check this other answer for more information.