在navbar Rails应用中显示购物车数量而不是购物车总价

Question

In my rails app I have this code in my _navbar.html.erb

            <% if @cart.total_price > 0 %>
                <%= link_to @cart do %> 
                    <i class="fa fa-shopping-cart"> &euro; </i>
                <%=  @cart.total_price %>
                <% end %>

                <% else %>
                    <a href="#" class="menu-cart"><i class="fa fa-shopping-cart"></i> &euro; 0.00</a>
                <% end %>

It displays the @cart.total_price but I want it to display the total items in the Cart instead.

I'm not sure how to do that

Most of this code is from a Udemy tutorial, but it's getting little bit to much for my experience so I feel kind a lost trying to modify this to my needs.

I've been trying to add the @product_item to the above code but with out a luck, can anyone take a look at this and guide me through this.

I have this code in the application_controller.rb

before_action :set_cart    

def set_cart
   @cart = Cart.find(session[:cart_id])
   rescue ActiveRecord::RecordNotFound
   @cart = Cart.create
   session[:cart_id] = @cart.id
end

In the carts_controller.rb I have this:

class CartsController < ApplicationController

before_action :set_cart, only: [:show, :destroy]
rescue_from ActiveRecord::RecordNotFound, with: :invalid_cart

def new
    @cart = Cart.new
end

def show
     @images  = ["1.jpg", "2.jpg", "3.jpg", "4.jpg", "5.jpg"]
 @random_no = rand(5)
 @random_image = @images[@random_no]

end


def destroy
    @cart.destroy if @cart.id == session[:cart_id]
    session[:cart_id] = nil
    redirect_to root_url, notice: 'Your Cart is Empty'
end


private

def set_cart
    @cart = Cart.find(params[:id])
end

def cart_params
    params[:cart]
end

def invalid_cart
    logger_error = 'You are trying to access invalid cart'
    redirect_to root_url, notice: 'Invalid Cart'
end
end

In the controllers/concerns I've this file current_cart.rb

module CurrentCart

private

def set_cart
    @cart = Cart.find(session[:cart_id])
    rescue ActiveRecord::RecordNotFound
    @cart = Cart.create
    session[:cart_id] = @cart.id
end
end

Then I have the product_items_controller.rb and there is this code:

class ProductItemsController < ApplicationController

include CurrentCart

before_action :set_cart, only: [:create]
before_action :set_product_item, only: [:show, :destroy]

def create

    @product = Product.find(params[:product_id])
    @product_item = @cart.add_product(@product.id)
    if @product_item.save
        redirect_to root_url, notice:'Product added to Cart'
    else
        render :new
    end
end

private

def set_product_items
    @product_item = ProductItem.find(params[:id])
end

def product_item_params
    params.require(:product_item).permit(:product_id)
end

end

And the relevant models are cart.rb and product_item.rb

in the cart.rb I have this code:

class Cart < ActiveRecord::Base

has_many :product_items, dependent: :destroy

def add_product(product_id)
    current_item = product_items.find_by(product_id: product_id)
    if current_item
        current_item.quantity += 1
    else
        current_item = product_items.build(product_id: product_id)
    end
    current_item
end

def total_price
    product_items.to_a.sum{|item| item.total_price}
end

end

And in the product_item.rb there is this code:

class ProductItem < ActiveRecord::Base
 belongs_to :product
 belongs_to :cart
 belongs_to :order


 def total_price
    product.price * quantity
 end

end

Answer 1

You can rewrite the @cart code in the _navbar.html.erb to look like this, it should work just like the previous chunk but shows the product_items.count instead of the total_price

<% if @cart.product_items.count > 0 %>
  <%= link_to @cart do %> 
  <i class="fa fa-shopping-cart"></i>
  <%= @cart.product_items.count %>
  <% end %>

  <% else %>
     <a href="#" class="menu-cart"><i class="fa fa-shopping-cart"></i> 0 </a>
<% end %>    

Answer 2

If you want total items in the cart, just take the sum of the quantity column over product_items in your Cart model, like this:

def total_quantity
  product_items.sum(:quantity)
end

Then you can just call @cart.total_quantity from the view (or anywhere else).

Note that by calling sum on product_items , which is a relation (and not an array), this directly calculates the sum using SQL:

SELECT SUM(`product_items`.`quantity`) FROM product_items
  WHERE `product_items`.`cart_id` = 123

where 123 is the id of the cart.

This is more efficient than calling sum on an array of product items (ie product_items.to_a.sum(&:quantity) ), which would load each product item, then sum the quantities. But either should work, and depending on what you're doing the latter sum may suit your needs better.