Ruby on Rails: wrong number of arguments (given 0, expected 1)

Question

I have an issue with my add_item method and have trouble to understand why.

Here is my carts_controller.rb

class CartsController < ApplicationController
  def index
    @cart_items = CartItem.all
  end

  def add_item
    @cart_item = CartItem.new
    produit_id = params[:produit_id]
    @cart_item = CartItem.find_or_create_by(params[:produit][:produit_id])
    @cart_item.save

    binding.pry
  end
end

Here is produits/index.html.erb (where the issue comes from)

<div id="produits-column-container">
  <% if @produits %>
    <% @produits.in_groups_of(4, false).each do |g| %>
      <% g.each do |produit| %>
      <div id="produits-row-container">
        <div id="fiche-produit-container">
            <div id="produit-img">
              <%= image_tag produit.photo %>
            </div>
            <div id="produit-nom">
              <%= produit.nom %>
            </div>
            <div id="produit-prix">
              <%= number_to_currency(produit.prix, unit: '€', format: "%n%u") %>
            </div>
            <div id="produit-au-panier">
              <%= image_tag('icon/icon-panier') %>
              <%= link_to 'Ajouter au panier', carts_add_item_path, method: :post %>
            </div>
         </div>
       </div>
      <% end %>
    <% end %>
  <% end %>
</div>

The error i'm given is :

ArgumentError in CartsController#add_item
wrong number of arguments (given 0, expected 1)

in def add_item(produit_id)

add_item(produit_id) is related to carts_add_item_path

I also give you the routes :

Rails.application.routes.draw do

  match "/mon-panier" => 'carts#index', via: :get

  post 'carts/add_item' => 'carts#add_item'

  resources :categories do
    resources :produits
  end

  resources :order_abonnements, only: [:create, :update, :delete]

  get 'livraisons_type/index'

  match "/recapitulatif" => 'recapitulatif#index', via: :get

  match "/confirmation-carte-cadeau" => 'recapitulatif#confirmation', via: :get

  match "/livraison-carte-cadeau" => 'livraison_carte#index', via: :get

  match '/activation-carte' => 'code_carte_cadeau#index', via: :get

  match "/offrir-une-box-bretonne" => 'cadeau#index', via: :get

  resources :order_items, only: [:create, :update, :destroy]

  match "/nos-box" => 'nos_box#index', via: :get

  get 'categories/index'

  devise_for :admin_users, ActiveAdmin::Devise.config
  ActiveAdmin.routes(self)

  match '/informations-penn-ar-box' => 'informations_penn_ar_box#index', via: :get

  match '/livraison-box-bretonne' => 'livraison_box_bretonne#index', via: :get

  match '/abonnements' => 'abonnements#index', via: :get

  devise_for :users, path: '', path_names: { sign_in: 'connexion', sign_out: 'déconnexion'}

  resources :users do
    delete 'déconnexion' => 'devise/sessions#destroy'
  end

  match '/mon-marche-breton' => 'marche_breton#index', via: :get

  root 'home#home'
end

And the logs :

Started POST "/carts/add_item" for ::1 at 2017-05-30 09:48:52 +0200
Processing by CartsController#add_item as HTML
  Parameters: {"authenticity_token"=>"QrToQUHVxjuV5cUvZYHd7tj457htfZohOkmsvNDnKv79P413xjsSfR/8RVXtdIU7/wcmhcxjkU85N13CqJkG2w=="}
  Cart Load (0.3ms)  SELECT  `carts`.* FROM `carts` WHERE `carts`.`id` = 1 LIMIT 1
Completed 500 Internal Server Error in 27ms (ActiveRecord: 14.9ms)

ArgumentError (wrong number of arguments (given 0, expected 1)):
  app/controllers/carts_controller.rb:6:in `add_item'

Solution

You need to pass produit_id as a parameter.

So change this line as so...

<%= link_to 'Ajouter au panier', 
            carts_add_item_path(produit_id: produit.id), method: :post %>

And change your controller method as so...

def add_item
  produit_id = params[:produit_id]
  ...

And change the find_or_create to

@cart_item = CartItem.find_or_create_by(produit_id: produit_id)

This does mean that you can only have one CartItem in your entire application that points to a product... strange design.

Comments

[Sergio Tulentsev]

Controller actions are not your ordinary ruby methods and they don't accept parameters like that, in the signature. You're supposed to read params[:produit_id] in the method body.

[Aleksei Matiushkin]

@SergioTulentsev well, controller actions are ordinary ruby methods after all, they just are called by the engine in some ways that the engine wants to call them.

[Sergio Tulentsev]

@mudasobwa: you know what I meant. :)

[justinedps26]

@SergioTulentsev what do i need to write to fix the issue? i'm in a hurry :)

[Sergio Tulentsev]

@justinedps26: the answer is in the last sentence of my comment

[justinedps26]

@SergioTulentsev i did write your way but nothing changed

[Sergio Tulentsev]

@justinedps26 you forgot to remove the parameter from the signature?

[Sergio Tulentsev]

@justinedps26: def add_item(produit_id) should be def add_item

[zauzaj]

@justinedps26 as @SergioTulentsev explained, controller actions don't receive parameters; as you can see you even don't use such parameter in action body but you access to params. So just remove parameter from method signature and bug will be solved !

[justinedps26]

@SergioTulentsev now i have undefined local variable or method cart_items'`

[Sergio Tulentsev]

@justinedps26: well, that's another issue, which doesn't have anything to do with the original error.

[justinedps26]

@SergioTulentsev well, i'll try to figure it out. Thanks for your help

[Sergio Tulentsev]

Now the question is wrong. The code given can't produce stated error. And, as a general rule, you must not edit questions like that (so that it becomes another question entirely). This invalidates existing answers.

[justinedps26]

@SergioTulentsev okay sorry, i just did that to be more clear in the comments

[Sergio Tulentsev]

@justinedps26: no problem. But do keep that in mind.

[justinedps26]

Let us continue this discussion in chat.

[Sergio Tulentsev]

That'll be useful, yes, but it's not the cause of the exact problem in the question.

[justinedps26]

Thanks, can you let me know the other things that are wrong please?

[SteveTurczyn]

? @SergioTulentsev surely it is? He's calling carts_add_item_path which resolves into a call to add_item without arguments. HIs definition of the add_item action expects an argument. Wrong number of arguments, given 0, expected 1.

[Sergio Tulentsev]

No, invocation of carts_add_item_path does not end up with a call to add_item.

[Sergio Tulentsev]

Ah, I see where I could be misunderstood. I was referring to the first part of the answer, the one with carts_add_item_path(produit_id: produit.id). If you do only that (pass parameter this way) and leave the action signature intact, you'll still see the error.

[Sergio Tulentsev]

(took the liberty to format some code. Horizontal scrolling on one-line snippets is horrible)

[justinedps26]

@SergioTulentsev the error went away but i now have undefined method []' for nil:NilClass`

[SteveTurczyn]

That's on line 7? Did you spell "params" correctly?

[SteveTurczyn]

I just realised you're not even using the argument! Just remove it from the def add_item line.

[SteveTurczyn]

@SergioTulentsev Yes, my answer was to do both steps, I wasn't giving OP a choice. Good improvement on the formatting, I'll remember that for future.

[SteveTurczyn]

And which line is the error? Does it say app/controllers/carts_controller.rb:8:in add_item or `app/controllers/carts_controller.rb:9:in add_item' ?

[justinedps26]

@SteveTurczyn it says app/controllers/carts_controller.rb:9:in add_item' `

[justinedps26]

Let us continue this discussion in chat.