ActionController::RoutingError (No route matches [POST] "/cars/1/consumptions/new"): - ruby-on-rails

Question

I have this routing error when I add a consumption (after submit it fails) and I am stuck, What am I doing wrong?
A user can have several cars and for each of his car he wants to look after his gas consumptions.
I have three active record models
create_table "cars", force: :cascade do |t|
t.string "car_name"
t.integer "user_id"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "consumption_searches", force: :cascade do |t|
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
end
create_table "consumptions", force: :cascade do |t|
t.float "total_price"
t.float "kilometers"
t.string "shop"
t.float "liter_price"
t.float "total_liters"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.integer "car_id"
end
create_table "users", force: :cascade do |t|
t.string "email", default: "", null: false
t.string "encrypted_password", default: "", null: false
t.string "reset_password_token"
t.datetime "reset_password_sent_at"
t.datetime "remember_created_at"
t.datetime "created_at", null: false
t.datetime "updated_at", null: false
t.index ["email"], name: "index_users_on_email", unique: true
t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
end
car belongs_to :users and has_many :consumptions
user has_many :cars, and has_many :consumptions through: :cars
consumption belong_to :car and belongs_to :user
My create method in consumptions_controller.rb
def create
#car = Car.find(params[:car_id])
#consumption = Consumptions.new(consumption_params)
#consumption.car = #car
if #consumption.save!
redirect_to car_consumptions_path, notice: 'consumption was successfully created.'
else
render :new
end
end
cars_controller.rb
def show
#car = Car.find(params[:id])
#search = ConsumptionSearch.new(params[:search])
#consumptions = #search.date_range
#consumptions = #consumptions.order('created_at ASC').where(car_id: #car.id)
end
views/consumptions/_form.html.erb
<%= simple_form_for car_consumptions_path do |f| %>
...
<% end %>
routes.rb
Rails.application.routes.draw do
devise_for :users
root to: "cars#index"
resources :cars do
resources :consumptions
end
end
rails routes | grep consumption
car_consumptions GET /cars/:car_id/consumptions(.:format) consumptions#index
POST /cars/:car_id/consumptions(.:format) consumptions#create
new_car_consumption GET /cars/:car_id/consumptions/new(.:format) consumptions#new
edit_car_consumption GET /cars/:car_id/consumptions/:id/edit(.:format) consumptions#edit
car_consumption GET /cars/:car_id/consumptions/:id(.:format) consumptions#show
PATCH /cars/:car_id/consumptions/:id(.:format) consumptions#update
PUT /cars/:car_id/consumptions/:id(.:format) consumptions#update
DELETE /cars/:car_id/consumptions/:id(.:format) consumptions#destroy
As requested
EDIT
here is what I have in the HTML if it can help:
<form novalidate="novalidate" class="simple_form /cars/1/consumptions" action="/cars/1/consumptions/new" accept-charset="UTF-8" method="post"><input name="utf8" type="hidden" value="✓"><input type="hidden" name="authenticity_token" value="0nwq/pQSXCU2ptBjbewTCBffPLpZZUPAj6/HPQTGtYd8cHz9zv8R/C/JYnXPDpKw5o3/vGlVtav2Sa2nSvgOQdQ==">

Answer 1

Lets start with the controller
# GET /cars/:car_id/consumptions/new
def new
#car = Car.find(params[:car_id])
#consumption = #car.consumptions.new
end
# POST /cars/:car_id/consumptions
def create
#car = Car.find(params[:car_id])
#consumption = #car.consumptions.new(consumption_params)
# `.save!` will raise an exception and blow up if the record is invalid.
# Not good.
if #consumption.save
redirect_to car_consumptions_path(#car), notice: 'consumption was successfully created.'
else
render :new
end
end
Note the redirect:
# consumptions#index
redirect_to car_consumptions_path(#car), notice: 'consumption was successfully created.'
Since this is a nested route you need to provide the car_id segment.
You could also redirect to:
# consumptions#show
redirect_to [#car, #consumption], notice: 'consumption was successfully created.'
# or to cars#show
redirect_to #car, notice: 'consumption was successfully created.'
When using simple_form_for you pass it model instances that it binds the form to. When creating forms for nested routes you should pass an array:
<%= simple_form_for([#car, #consumption]) do |f| %>
<% end %>
This uses the polymorphic route helpers to find the correct path. You can use this same signature for link_to, redirect_to, url_for and path_for.
When declaring nested routes you should consider using the shallow option. It will only nest the collection routes (new, create, index) and not the member routes.

Answer 2

Try this:
<%= form_for [#cars, #consumptions] do |form| %>
...
<% end %>
or
<%= form_with(model: [ #cars, #consumptions ]) do |form| %>
*** Update:
resources :cars, shallow: true do
resources :consumptions
end
Into form:
<% = simple_form_for [#car, #consumption] do |f| %>

Answer 3

You are not showing your new action, but I assume you are setting a #car and a #consumption = #car.consumptions.build variables.
Try with this:
simple_form_for #consumption, url: url_for(controller: :consumptions, action: :create, car_id: #car.id) do |f|
It should work with simple_form_for [#car, #consumption] do |f| but you said "it doesn't work" which is too ambiguous (how does that not work? same error? new error? you should be more clear when responding to answers)

Answer 4

car_consumptions_path != car_consumption_path
I don't see any "car_consumptions" in your routes.