NameError in Categories#show

Question

So I have products and cart system in my rails app. Now I'm trying to create custom page, under custom controller, to showcase each product from certain category. When I include a form_for into a div class of a product, (in order to submit a form and move product to a cart), I get this error:

Showing /home/ubuntu/workspace/app/views/categories/show.html.erb where line #28 raised:

undefined local variable or method `order_item' for #<#<Class:0x007fd83dfbdea8>:0x007fd85cbad0b0>
Did you mean?  order_item_url

This is the form that shows error on app/views/categories/show.html.erb:

<%= form_for order_item, remote: true do |f| %>
      <h4 class="text-right">Unit Price: <span style="color: green"><%= number_to_currency product.price %></span></h4>
        <div class="input-group">
          <%= f.number_field :quantity, value: 1, class: "form-control", min: 1 %>
          <div class="input-group-btn">
            <%= f.hidden_field :product_id, value: product.id %>
            <%= f.submit "Add to Cart", class: "btn btn-primary" %>
          </div>
        </div>
      <% end %>

These are my controllers:

class ProductsController < ApplicationController
  def index
    @products = Product.all
    @order_item = current_order.order_items.new
  end

  def new
    @product = Product.new @categories = Category.all.map{|c| [ c.name, c.id ] }
  end


  def create 
   @product = Product.new(product_params) 
   @product.category_id = params[:category_id] 
   respond_to do |format| 
   if @product.save 

      format.json { render :show, status: :created, location: @product } 
   else 
       format.html { render :new } 
       format.json { render json: @product.errors, status: :unprocessable_entity } 
   end 
  end 
end

def edit
  @categories = Category.all.map{|c| [ c.name, c.id ] }
end

def update 
  @product.category_id = params[:category_id]
end


end

order_items_controller.rb:

class OrderItemsController < ApplicationController
  def create
    @order = current_order
    @order_item = @order.order_items.new(order_item_params)
    @order.user_id = current_user.id
    @order.save
    session[:order_id] = @order.id
  end



  def update
    @order = current_order
    @order_item = @order.order_items.find(params[:id])
    @order_item.update_attributes(order_item_params)
    @order_items = @order.order_items
  end



  def destroy
    @order = current_order
    @order_item = @order.order_items.find(params[:id])
    @order_item.destroy
    @order_items = @order.order_items
  end
private
  def order_item_params
    params.require(:order_item).permit(:quantity, :product_id, :user_id)
  end
end

and associated routes:

Rails.application.routes.draw do

  resources :categories
  resources :products, only: [:index]
  resource :cart, only: [:show]
  resources :order_items, only: [:create, :update, :destroy, :new]
  root to: "products#index"

Answer 1

You are in a view belonging to the Categories controller.

You need to add, in your show action of the categories controller:

# CategoriesController
def show
 @order_item = OrderItem.new # Add this line
 # rest of your code
end

And replace in your form_for order_item by @order_item