Why are listings not saved in category?

Rails
1

Hello everyone,

I’m currently working on the functionality that users can create
listings that are than saved in categories. I created tables and
relationships but I cannot get the listings do be saved in the
categories.
Here is what I have:

Model category.rb

class Category < ActiveRecord::Base
has_many :listings
end

model listing.rb
class Listing < ActiveRecord::Base
belongs_to :user
belongs_to :category
default_scope -> { order(‘created_at DESC’) }
validates :location, presence: true, length: { maximum: 20 }
validates :title, presence: true, length: { maximum: 20 }
validates :user_id, presence: true
validates :description, presence: true

end

Listings controller
def new
@listing = Listing.new
@listings = Listing.paginate(page: params[:page])
@categories = Category.all
end

def create
@listing = current_user.listings.build(listing_params)
@categories = Category.all
if @listing.save
flash[:success] = “Job Post created”
redirect_to current_user
else
render ‘listings/new’
end
end

Views categories/new

New category

<%= render ‘form’ %>

<%= link_to ‘Back’, categories_path %>

Views categories/_form.html.erb
<%= form_for(@category) do |f| %>
<% if @category.errors.any? %>


<%= pluralize(@category.errors.count, “error”) %> prohibited
this category from being saved:

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

<% end %>

<%= f.label :name %>
<%= f.text_field :name %>
<%= f.submit %>
<% end %>

Views Listing/new.html.erb

<%= form_for(@listing) do |f| %> <%= render 'shared/error_messages', object: f.object %>

Create Job Post 

<%= f.label :title %>
<%= f.text_field :title %>

<%= f.label :location %>
<%= f.text_field :location %>
<br>

  <%= f.text_area :description, placeholder: "Compose new

listing…", class: “description_form” %>

Category:
<% @categories.each do |category| %> > <%= category.name %> <% end %>

<%= f.submit "Post", class: "tfbutton tfbutton-search tfbutton-sign-up post" %>

<% end %>

I have a listings table with the following columns:
id title description location user_id created_at updated_at category_id

and categories table
id name created_at updated_at

When I create a new listing and than check the listings table, the
category_id field is blank.
Does anyone know why my listings are not saved in the categories?

Thank you very much