更改Rails购物车中的数量

# 购物车模型
class Cart < ApplicationRecord
  has_many :cart_items
end

# 购物车项模型
class CartItem < ApplicationRecord
  belongs_to :cart
  belongs_to :product
end

# 购物车控制器
class CartsController < ApplicationController
  def update_quantity
    cart = Cart.find(params[:id])
    cart_item = cart.cart_items.find(params[:cart_item_id])
    cart_item.quantity = params[:quantity]
    cart_item.save

    redirect_to cart_path(cart)
  end
end

# 购物车视图页面
<%= form_with(model: cart, url: update_quantity_cart_path(cart)) do |form| %>
  <%= form.hidden_field :id %>
  <%= form.hidden_field :cart_item_id %>
  <%= form.number_field :quantity %>
  <%= form.submit "Update Quantity" %>
<% end %>