Rails Nested Attributes with has_many through association not creating - ruby-on-rails

Question

I am trying to provide a way to generate a new object ("List") in one model with a new associated object in another ("Item") using a has_many through relationship (through "Groupings"). I was able to get the form working fine but can't figure out what I'm missing in order to finish the creation process correctly.
Rails v. 5.1.2, Ruby v. 2.4.1
lists_controller.rb
def new
#list = current_user.lists.new
3.times { #list.items.build }
end
def create
#list = current_user.lists.new(list_params)
respond_to do |format|
if #list.save
format.html { redirect_to #list, notice: 'List was successfully created.' }
format.json { render :show, status: :created, location: #list }
else
format.html { render :new }
format.json { render json: #list.errors, status: :unprocessable_entity }
end
end
end
private
def set_list
#list = List.find(params[:id])
end
def correct_user
#list = current_user.lists.find_by(id: params[:id])
redirect_to lists_path, notice: "Not authorized to edit this list"
if #list.nil?
end
def list_params
params.require(:list).permit(:title, {
item_attributes: [
:id, :title, :url
]})
end
items_controller.rb
def new
#item = Item.new
end
private
def set_item
#item = Item.find(params[:id])
end
def item_params
params.require(:item).permit(:title, :body, :url, :created,
:list_ids => [])
end
end
list.rb model
has_many :groupings, :dependent => :destroy
has_many :items, :through => :groupings
accepts_nested_attributes_for :items,
reject_if: ->(attrs) { attrs['title'].blank? || attrs['url'].blank? }
item.rb model
has_many :groupings, :dependent => :destroy
has_many :lists, :through => :groupings
validate :has_lists?
accepts_nested_attributes_for :lists
attr_writer :list_titles
after_save :assign_lists
def list_titles
#list_titles || lists.map(&:title).join(' ')
end
private
def assign_lists
if #list_titles
self.lists = #list_titles.split(/\,/).map do |title|
if title[0..0]==" "
title=title.strip
end
title=title.downcase
List.find_or_create_by_title(title)
end
end
end
def has_lists?
errors.add(:base, 'This item needs to be assigned to a list before it can be saved.') if self.lists.blank?
end
grouping.rb model
belongs_to :item
belongs_to :list
accepts_nested_attributes_for :item, :list
Lists Form
<%= form_with(model: list, local: true) do |f| %>
<% if list.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(list.errors.count, "error") %> prohibited this list from being saved:</h2>
<ul>
<% list.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= f.label :title %>
<%= f.text_field :title, id: :list_title %>
</div>
<div>
<p><strong>Items:</strong></p>
<%= f.fields_for :items do |item| %>
<div>
<%= item.label :title %>
<%= item.text_field :title %>
<%= item.label :url %>
<%= item.text_field :url %>
</div>
<% end %>
</div>
<div class="actions">
<%= f.submit %>
</div>
<% end %>
Sample Console Output
Started POST "/lists" for 127.0.0.1 at 2017-09-19 13:12:53 -0700
Processing by ListsController#create as HTML
Parameters: {"utf8"=>"✓", "authenticity_token"=>"Y6rszWVUXDIVymuoBkXwvkw1pVbyC6mffiWIZzr7PVd1NT9JJi6rD72k5Fh2qU5Q5tEd0qn6bFYMSJnz2TgjAA==", "list"=>{"title"=>"Websites", "items_attributes"=>{"0"=>{"title"=>"Google", "url"=>"www.google.com"}, "1"=>{"title"=>"Yahoo", "url"=>"www.yahoo.com"}, "2"=>{"title"=>"Bing", "url"=>"www.bing.com"}}}, "commit"=>"Create List"}
User Load (0.3ms) SELECT "users".* FROM "users" WHERE "users"."id" = $1 ORDER BY "users"."id" ASC LIMIT $2 [["id", 2], ["LIMIT", 1]]
Unpermitted parameter: :items_attributes
(0.1ms) BEGIN
SQL (0.9ms) INSERT INTO "lists" ("title", "created_at", "updated_at", "user_id") VALUES ($1, $2, $3, $4) RETURNING "id" [["title", "Websites"], ["created_at", "2017-09-19 20:12:53.458577"], ["updated_at", "2017-09-19 20:12:53.458577"], ["user_id", 2]]
(0.3ms) COMMIT
Redirected to http://localhost:3000/lists/24
Completed 302 Found in 7ms (ActiveRecord: 1.6ms)
I'm still learning, clearly - but after trying all kinds of related hints on this forum I couldn't figure this one out. Thanks for any help!

Answer 1

You're almost there but there is an error being reported in your console logs: Unpermitted parameter: :items_attributes.
Change item_attributes to items_attributes in your list_params:
def list_params
params.require(:list)
.permit(:title, items_attributes: [:id, :title, :url])
end

Answer 2

You have some mistakes in your syntax when you define your params. It should be like this: (items instead item and you don't need {})
def list_params
params.require(:list).permit(:title,
items_attributes: [:id, :title, :url])
end