NoMethodError for new controller in Rails - ruby-on-rails

Question

Cities#new controller shows error involving cities_path, but I don't have it in any file nor in CitiesController. I checked all files, tried to restart the server but still nothing.
undefined method `cities_path' for #<#<Class:0x007f9e4c1cb348>:0x00000003836140>
Did you mean? city_path
CitiesController
class CitiesController < ApplicationController
def index
#cities = City.all
end
def show
find_city
end
def new
#city = City.new
end
def edit
find_city
end
def update
find_city
if #city.save
redirect_to city_path(#city)
else
render "edit"
end
end
def create
#city = City.new(city_params)
if #city.save
redirect_to index_path
else
render "new"
end
end
private
def find_city
#city = City.find(params[:id])
end
def city_params
params.require(:city).permit(:name, :icon_url)
end
end
Routes
get "/cities/new" => "cities#new", as: "new_city"
post "/index" => "cities#create"
get "/cities/:id" => "cities#show", as: "city"
get "/cities/:id/edit" => "cities#edit", as: "edit_city"
patch "/city/:id" => "cities#update"
Form (error is raised on first line)
<%= form_for #city do |f| %>
<% if #city.errors.any? %>
<div class="errors">
<ul>
<% city.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<%= f.label "Name:" %>
<%= f.text_field :name, class: "form-control" %>
<%= f.label "Icon:" %>
<%= f.text_field :icon_url, class: "form-control" %>
<%= f.submit "Pošalji" %>
<% end %>

Answer 1

When you use form_for #city, and #city is a new record, form_for will try to find a cities_path to POST the new attributes back to.
You should be using resources :cities in your routes file to automatically define the routes and their names. If you want to define a limited set of routes, you can use :only or :except:
resources :cities, only: %i(new create show edit update)
If you don't use resources, you either need to explicitly specify a path for your form_for call, or you need to provide a route named cities_path manually:
post "/index" => "cities#create", as: :cities
Note that index routes don't typically actually contain the word index, you should really just be posting to /cities, not /index.
post "/cities" => "cities#create", as: :cities