没有为 nil 实现协议 Enumerable (phoenix-framework)

Question

我在订单控制器中添加了“支付”功能，并为此添加了路由。

def payment(conn, %{"id" => id}) do
  foods = Repo.all(Food)
  order =
    Repo.get!(assoc(conn.assigns[:table], :orders), id)
    |> Repo.preload(order_items: :food)
  order_item_changeset =
    order
    |> build_assoc(:order_items)
    |> Pos1.OrderItem.changeset()
  order_changeset = Order.changeset(order)

  render(conn, "payment.html", order: order, order_item_changeset: order_item_changeset, order_changeset: order_changeset, foods: foods, payment: @payment)
end

resources "/tables", TableController do
  resources "/orders", OrderController do
    get "/payment", OrderController, :payment
end

我在表和订单下添加了付款路线，因为付款必须显示其表号和订单 ID。我在订单模板的 show.html 中添加了支付页面的链接。但是，它会导致 Protocol.UndefinedError。

[error] #PID<0.9096.0> running Pos1.Endpoint terminated
Server: localhost:4000 (http)
Request: GET /tables/1/orders/14
** (exit) an exception was raised:
    ** (Protocol.UndefinedError) protocol Enumerable not implemented for nil
        (elixir) lib/enum.ex:1: Enumerable.impl_for!/1
        (elixir) lib/enum.ex:116: Enumerable.reduce/3
        (elixir) lib/enum.ex:1486: Enum.reduce/3
        (pos1) Pos1.Router.Helpers.segments/3
        (pos1) web/router.ex:1: Pos1.Router.Helpers.table_order_order_path/5
        (pos1) web/templates/order/show.html.eex:59: Pos1.OrderView."show.html"/1
        (pos1) web/templates/layout/app.html.eex:41: Pos1.LayoutView."app.html"/1
        (phoenix) lib/phoenix/view.ex:344: Phoenix.View.render_to_iodata/3
        (phoenix) lib/phoenix/controller.ex:633: Phoenix.Controller.do_render/4
        (pos1) web/controllers/order_controller.ex:1: Pos1.OrderController.action/2
        (pos1) web/controllers/order_controller.ex:1: Pos1.OrderController.phoenix_controller_pipeline/2
        (pos1) lib/phoenix/router.ex:261: Pos1.Router.dispatch/2
        (pos1) web/router.ex:1: Pos1.Router.do_call/2
        (pos1) lib/pos1/endpoint.ex:1: Pos1.Endpoint.phoenix_pipeline/1
        (pos1) lib/plug/debugger.ex:93: Pos1.Endpoint."call (overridable 3)"/2
        (pos1) lib/phoenix/endpoint/render_errors.ex:34: Pos1.Endpoint.call/2
        (plug) lib/plug/adapters/cowboy/handler.ex:15: Plug.Adapters.Cowboy.Handler.upgrade/4
        (cowboy) src/cowboy_protocol.erl:442: :cowboy_protocol.execute/4

我该如何解决这个问题？我应该使用其他方法来定义功能支付吗？

这是来自 web/templates/order/show.html.eex:59 的代码

 <%= link "Confirm orders", to: table_order_order_path(@conn, :payment, @table, @order, @payment) %> 




<%= if @payment do %>
<%= link "Confirm orders", to: table_order_order_path(@conn, :payment, @table, @order, @payment) %>
<% end %>

Answer 1

错误protocol Enumerable not implemented for nil 表示您将nil 传递到应该使用列表或枚举的地方。

如果你向下看堆栈，你可以看到它是：Pos1.Router.Helpers.table_order_order_path/5 订单路径可能需要订单或订单 ID，即数据库中的 NULL。您可以简单地尝试在控制器中打印order和order_item_changeset，看看哪个有问题。

如果你再看低一点，它会告诉你你的问题在于模板：web/templates/order/show.html.eex:59。在你的模板中试试这个：

<%= if @order do %> #or whichever value is nil
  your code here
<% end %>