Rails - Problem with passing local variables - ruby-on-rails

Question

I'm running Rails 6.0.3.2 and I want to render a partial passing a local variable to another controller view:
My routes:
Rails.application.routes.draw do
devise_for :users
root to: 'notebooks#index'
resources :notebooks, only: [:index, :new, :show, :create, :edit, :update, :destroy] do
# For details on the DSL available within this file, see https://guides.rubyonrails.org/routing.html
collection do
get "list"
end
end
resources :tags
end
Notebook Model:
class Notebook < ApplicationRecord
has_one_attached :photo
validates :asin, presence: true, uniqueness: true
after_initialize :init
acts_as_list column: :position, add_new_at: :bottom
has_many :taggings
has_many :tags, through: :taggings
def init
self.edited ||= false
end
end
Tag Model
class Tag < ApplicationRecord
has_many :taggings
has_many :notebooks, through: :taggings
end
In Tag controller:
def index
#tags = Tag.all.order(created_at: :asc)
end
I tried to follow this guide and render the "index view" from Tags Controller on the "list view". The application finds the tags/_index.html file, but return the error undefined method `each' for nil:NilClass. Bellow my views code:
In app/views/notebooks/list.html.erb:
<%= render :partial => "tags/index" , locals: {tags: #tags}%>
In app/views/tags/_index.html.erb
<% tags.each do |tag| %>
<div>
<div class="d-flex">
<p><%= tag.id %></p>
<p><%= tag.name %></p>
</div>
<p>tag.taggings.count</p>
</div>
<% end %>
Anyone can point me what i'm doing wrong? I read the Layouts and Rendering in Rails documentation, but i don't have a clue why the instructions won't work on my project...
Thanks in advance!

Answer 1

The rails way to do this is just to create a partial for a single record:
# app/views/tags/_tag.html.erb
<div>
<div class="d-flex">
<p><%= tag.id %></p>
<p><%= tag.name %></p>
</div>
<p>tag.taggings.count</p>
</div>
You can then pass the collection to render and Rails will look up the partial and render it for each member in the collection:
<%= render #tags %>
This is short for:
<%= render partial: 'tag', collection: #tags %>
See Rendering Collections.