Rails：多步表单上的动态选择不保持选择

我正在按照瑞安·贝茨 (Ryan Bates) 的要求，为订单下达流程制定多步骤表单多步骤教程 #217它使用会话。第一步，我有两个选择字段：一个用于国家（陆地），一个动态用于运输服务。选择土地后，运输服务将通过 javascript/jQuery 加载到第二个选择字段中，并通过 JS 计算总价。

应用程序/视图/订单/_shipping_step.html.erb

<%= f.collection_select(:land_id, Land.all, :id, :name, {:prompt => "select a country"}, {:id => 'lands_select'}) %>
<%= f.select(:shippingservice_id, options_for_select(@shippingservices.collect { |s| [s.name.titleize, s.id, {'data-price' => s.price}] }, :selected => f.object.shippingservice_id), {:prompt => "select a carrier"}, {:id => "shippingservices_select"}) %>

阿贾克斯脚本

$(document).on("change", "#lands_select", function(event){
  $.ajax({
    url: "/carts/update_shipping/" + event.target.value,
    type: "GET",
  })
});

在多步骤表单的运输详细信息步骤中，我可以选择陆运，相应的运输选项已加载，我可以选择一个。当进行到付款步骤时，我可以下订单并且一切正常，但如果我想从付款步骤返回到订单步骤以更改某些内容，运输服务选择器会显示 land_id = 1 的选项，而土地选择显示选择的国家/地区，例如 id 85。

I added :selected => session[:cart_params]到运输服务选择，但它似乎不起作用。:selected => f.object.shippingservice_id保留优先或标准运输选项，但适用于 Land_id 1。

我怎样才能让它发挥作用？是选择字段还是JS？为什么第二个选择不将所选土地保留在内存中？

先感谢您！

LOG:

Started GET "/orders/new" for 127.0.0.1 at Thu Dec 27 22:08:52 +0100 2018
Processing by OrdersController#new as HTML
  Cart Load (0.3ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (1.4ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.3ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  CACHE (0.0ms)  SELECT `lands`.* FROM `lands` 
  Shippingservice Load (0.6ms)  SELECT `shippingservices`.* FROM `shippingservices` INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` WHERE `lands`.`id` = 1 AND (weightmin <= 50 AND weightmax >= 50 AND heightmin <= 3 AND heightmax >= 3 AND shippingservices.shippingcarrier = ‘1’) AND (lengthmax >= 210 AND widthmax >= 149)
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 3 LIMIT 1
  Hero Load (0.2ms)  SELECT `heros`.* FROM `heros` WHERE `heros`.`id` = 18 LIMIT 1
  Rendered orders/_shipping_step.html.erb (13.7ms)
  Rendered orders/new.html.erb within layouts/application (16.2ms)
  Rendered layouts/_header.html.erb (0.1ms)
  Rendered layouts/_footer.html.erb (0.1ms)
Completed 200 OK in 44ms (Views: 23.0ms | ActiveRecord: 3.9ms)

选择运送国家：

Started GET "/carts/update_shipping/85" for 127.0.0.1 at Thu Dec 27 22:09:27 +0100 2018
Processing by CartsController#update_shipping as */*
  Parameters: {"id"=>"85"}
  Cart Load (0.2ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (66.9ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.4ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  Shippingservice Load (0.6ms)  SELECT `shippingservices`.* FROM `shippingservices` INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` WHERE `lands`.`id` = 85 AND (weightmin <= 50 AND weightmax >= 50 AND heightmin <= 3 AND heightmax >= 3 AND shippingservices.shippingcarrier = ‘1’) AND (lengthmax >= 210 AND widthmax >= 149)
  Rendered carts/_shippingservice.html.erb (0.2ms)
  Rendered carts/update_shipping.js.erb (2.9ms)
Completed 200 OK in 87ms (Views: 7.8ms | ActiveRecord: 68.6ms)

进入下一步：

Started POST "/orders" for 127.0.0.1 at Thu Dec 27 22:09:33 +0100 2018
Processing by OrdersController#create as HTML
  Parameters: {"order"=>{"ship_to_last_name"=>”surname”, "ship_to_address"=>”street”, "ship_to_city"=>”city”, "ship_to_postal_code"=>”postcode”, "phone_number"=>”somenumber”, "shippingservice_id"=>"27", "email"=>”[email protected]”, "land_id"=>"85", "ship_to_first_name"=>”firstname”}, "authenticity_token"=>”somestring”, "utf8"=>"✓", "commit"=>"Continue"}
  Cart Load (0.2ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (1.5ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.4ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.2ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  Land Load (0.4ms)  SELECT `lands`.* FROM `lands` WHERE `lands`.`id` = 85 LIMIT 1
  Shippingservice Load (0.3ms)  SELECT `shippingservices`.* FROM `shippingservices` WHERE `shippingservices`.`id` = 27 LIMIT 1
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 3 LIMIT 1
  Hero Load (0.3ms)  SELECT `heros`.* FROM `heros` WHERE `heros`.`id` = 18 LIMIT 1
  Rendered orders/_payment_step.html.erb (7.0ms)
  Rendered orders/new.html.erb within layouts/application (8.9ms)
  Rendered layouts/_header.html.erb (0.1ms)
  Rendered layouts/_footer.html.erb (0.0ms)
Completed 200 OK in 39ms (Views: 13.7ms | ActiveRecord: 4.6ms)

返回到运输详细信息步骤：

Started POST "/orders" for 127.0.0.1 at Thu Dec 27 22:09:35 +0100 2018
Processing by OrdersController#create as HTML
  Parameters: {"authenticity_token"=>”somestring”, "utf8"=>"✓", "back_button"=>"Back"}
  Cart Load (0.3ms)  SELECT `carts`.* FROM `carts` WHERE `carts`.`id` = ? LIMIT 1  [["id", 1]]
  Land Load (2.4ms)  SELECT `lands`.* FROM `lands` 
  CartItem Load (0.5ms)  SELECT `cart_items`.* FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.3ms)  SELECT MAX(`cart_items`.`length`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
   (0.4ms)  SELECT MAX(`cart_items`.`width`) AS max_id FROM `cart_items` WHERE `cart_items`.`cart_id` = 1
  CACHE (0.0ms)  SELECT `lands`.* FROM `lands` 
  Shippingservice Load (0.7ms)  SELECT `shippingservices`.* FROM `shippingservices` INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` WHERE `lands`.`id` = 1 AND (weightmin <= 50 AND weightmax >= 50 AND heightmin <= 3 AND heightmax >= 3 AND shippingservices.shippingcarrier = ‘1’) AND (lengthmax >= 210 AND widthmax >= 149)
  Product Load (0.3ms)  SELECT `products`.* FROM `products` WHERE `products`.`id` = 3 LIMIT 1
  Hero Load (0.2ms)  SELECT `heros`.* FROM `heros` WHERE `heros`.`id` = 18 LIMIT 1
  Rendered orders/_shipping_step.html.erb (16.5ms)
  Rendered orders/new.html.erb within layouts/application (18.4ms)
  Rendered layouts/_header.html.erb (0.2ms)
  Rendered layouts/_footer.html.erb (0.1ms)
Completed 200 OK in 109ms (Views: 24.0ms | ActiveRecord: 5.1ms)

UPDATE

这是我的部分orders_controller.rb

before_filter :initialize_cart

def new
  session[:order_params] ||= {}
  @order = Order.new(session[:order_params])
  @order.current_step = session[:order_step]
  @shippingservices = @cart.available_shipping_services.joins(:lands).where(:lands => {:id => session[:cart_params]})
end

def create
  session[:order_params].deep_merge!(params[:order]) if params[:order]
  @order = Order.new(session[:order_params])
  @shippingservices = @cart.available_shipping_services.joins(:lands).where(:lands => {:id => session[:cart_params]})
  @order.current_step = session[:order_step]
  if @order.valid?
    if params[:back_button]
      @order.previous_step
    elsif @order.last_step? && params[:commit] == 'Option A'
      …
    elsif @order.last_step? && params[:commit] == 'Option B'
      …
    else
      @order.next_step
    end
    session[:order_step] = @order.current_step
  end
  if @order.new_record?
    render "new"
  else
    # Empty the cart
    @cart.cart_items.destroy_all
    # Reset session
    session[:order_step] = session[:order_params] = nil
  end
end

当我通过 Land.first.id 或 Land.last.id 指定 id 时，查询有效并且后退步骤似乎有效。

使用时session[:order_params] I get ActiveRecord::StatementInvalid in Orders#create但存在正确的 land_id：

Mysql::Error: Unknown column 'id.ship_to_last_name' in 'where clause': SELECT `shippingservices`.* FROM `shippingservices` 
INNER JOIN `zones` ON `zones`.`id` = `shippingservices`.`zone_id` 
INNER JOIN `lands_zones` ON `lands_zones`.`zone_id` = `zones`.`id` 
INNER JOIN `lands` ON `lands`.`id` = `lands_zones`.`land_id` 
WHERE `id`.`ship_to_last_name` = 'Smith' 
AND `id`.`ship_to_address` = 'Somewherestreet' 
AND `id`.`ship_to_city` = 'Nowheretown' 
AND `id`.`ship_to_postal_code` = '99999' 
AND `id`.`phone_number` = 'some number' 
AND `id`.`shippingservice_id` = '34' 
AND `id`.`email` = '[email protected]' 
AND `id`.`land_id` = '85' 
AND `id`.`ship_to_first_name` = 'John' 
AND (weightmin <= 200 AND weightmax >= 200 AND heightmin <= 12 AND heightmax >= 12 AND shippingservices.shippingcarrier = '1') AND (lengthmax >= 210 AND widthmax >= 149)

@shippingservices = @cart.available_shipping_services.joins(:lands).where(:lands => {:id => session[:cart_params]})

这是没有正确使用session[:cart_params]得到land_id以便在通过表单返回时设置订单。我们可以改为使用@order = Order.new(session[:order_params])定义上面一行来抓取@order.land_id并且不必依赖任何会话。

如果订单有可能在没有相应土地的情况下被初始化，我还会添加一个存在检查。