why is parameter being pass as "/"? - ruby-on-rails

Question

I have a products and categories controllers, when I create a new product, the :category_id is passed as "/". And I cannot figure out why. Routes.rb is fine, models are standard, and controller#create is ok (posted below). What could be wrong?
def new
#product = Product.new
end
def create
#product = Product.new(product_params)
#product.category_id = params[:category_id]
respond_to do |format|
if #product.save
format.html { redirect_to category_products_path(#category), notice: 'P$
format.json { render :show, status: :created, location: #product }
else
format.html { render :new }
format.json { render json: #product.errors, status: :unprocessable_enti$
end
end
end
_form.html.erb
<%= form_for [#category, #product], url: category_products_path([#category, #product]) do |form| %>
<% if product.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(product.errors.count, "error") %> prohibited this product from being saved:</h2>
<ul>
<% product.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= form.label :name %>
<%= form.text_field :name %>
</div>
<div class="actions">
<%= form.submit %>
</div>
<% end %>
rake routes:
category_products GET /categories/:category_id/products(.:format) products#index
POST /categories/:category_id/products(.:format) products#create
new_category_product GET /categories/:category_id/products/new(.:format) products#new
edit_category_product GET /categories/:category_id/products/:id/edit(.:format) products#edit
category_product GET /categories/:category_id/products/:id(.:format) products#show
PATCH /categories/:category_id/products/:id(.:format) products#update
PUT /categories/:category_id/products/:id(.:format) products#update
DELETE /categories/:category_id/products/:id(.:format) products#destroy

Answer 1

category_products_path([#category, Product.new]) #=> "categories/1%2f/products"
Where %2f code of /. [#category, Product.new] is an array and passes as a single parameter.
<%= form_for [#category, #product], url: category_products_path(#category, #product) do |form| %>
<% end %>
<%= form_for [#category, #product], url: category_products_path(#category) do |form| %>
<% end %>
<%= form_for [#category, #product], url: category_products_path(#category.id) do |form| %>
<% end %>
<%= form_for [#category, #product], url: category_products_path(category_id: #category.id) do |form| %>
<% end %>
Each would work.
Also, before redirect_to category_products_path(#category) #category not seted. So, change current path to:
redirect_to category_products_path(#product.category_id)
And update your action new:
def new
#category = Category.find_by(id: params[:category_id])
#product = Product.new
end

Answer 2

<%= form_for Product.new, url: category_products_path(params[:category_id]) do |form| %>
<% if product.errors.any? %>
<div id="error_explanation">
<h2><%= pluralize(product.errors.count, "error") %> prohibited this product from being saved:</h2>
<ul>
<% product.errors.full_messages.each do |message| %>
<li><%= message %></li>
<% end %>
</ul>
</div>
<% end %>
<div class="field">
<%= form.label :name %>
<%= form.text_field :name %>
</div>
<div class="actions">
<%= form.submit %>
</div>
<% end %>
Controller: -
def create
#product = Product.new(product_params)
#product.category_id = params[:category_id]
respond_to do |format|
if #product.save
format.html { redirect_to category_products_path(#product.category), notice: 'P$
format.json { render :show, status: :created, location: #product }
else
format.html { render :new }
format.json { render json: #product.errors, status: :unprocessable_enti$
end
end
end