Ruby on rails Stripe - set default amount to shopping cart subtotal -

i trying connect shopping cart stripe , set amount order subtotal of cart. tried defining order_subtotal in orders model , tried pass though amount field in stripe code following error when go through check out: invalid integer: order_subtotal

i cant find online explains how connect amount varies stripe using ruby language. appreciated, thanks!

charges_controller.rb

class chargescontroller < applicationcontroller     def new     end      def create       # amount in cents        @amount = :order_subtotal         customer = stripe::customer.create(         :email => params[:stripeemail],         :source  => params[:stripetoken]       )        charge = stripe::charge.create(         :customer    => customer.id,         :amount      =>  :order_subtotal,         :description => 'rails stripe customer',         :currency    => 'usd'       )      rescue stripe::carderror => e       flash[:error] = e.message       redirect_to new_charge_path     end end 

cart/show.html.erb

<div class="shopping-cart">   <%= render "shopping_cart" %> <%= form_tag charges_path %>   <article>     <% if flash[:error].present? %>       <div id="error_explanation">         <p><%= flash[:error] %></p>       </div>     <% end %>     <label class="amount">       <span>:order_subtotal</span>     </label>   </article>    <script src="https://checkout.stripe.com/checkout.js" class="stripe-button"           data-key=env[publishable_key]           data-description="checkout"           data-amount= "amount"           data-locale="auto"           data-shipping-address="null"           >   </script>            <% end %> </div> 

_shopping_cart.html.erb

<% if !@order_item.nil? && @order_item.errors.any? %>   <div class="alert alert-danger">     <ul>     <% @order_item.errors.full_messages.each |msg| %>       <li><%= msg %></li>     <% end %>     </ul>   </div> <% end %> <% if @order_items.size == 0 %>   <p class="text-center">     there no items in shopping cart.  please <%= link_to "go back", root_path %> , add items cart.   </p> <% else %>   <% @order_items.each |order_item| %>     <%= render 'carts/cart_row', product: order_item.product, order_item: order_item, show_total: true %>   <% end %>    <p class="text-center">order subtotal=<%= order_subtotal= @order_items.sum(:total_price)%></p>  <% end %> 

order.rb

class order < activerecord::base    belongs_to :order_status    has_many :order_items    before_create :set_order_status   before_save :update_subtotal       def subtotal     order_items.collect { |oi| oi.valid? ? (oi.quantity * oi.unit_price) : 0}.sum    end    def order_subtotal    @order_items.sum(:total_price)   end end private   def set_order_status     self.order_status_id = 1   end    def update_subtotal     self[:subtotal] = subtotal   end 

in charges_controller.rb replace

:amount => :order_subtotal 

with

:amount => order_subtotal 

you adding symbol instead of result of order_subtotal method.

also in cart/show.html.erb want

<span><%= order_subtotal %></span> 

instead of

<span>:order_subtotal</span> 

about line:

<p class="text-center">order subtotal=<%= order_subtotal= @order_items.sum(:total_price)%></p> 

since seem not have order instance when cart being charged for, cannot access order#order_subtotal method. it's therefore best have helper method cart_subtotal calculate displayed values instead of doing right in template.