video - 当我上传新视频时，它返回 "no function clause matching"错误

Question

我正在将 Elixir 用于一个带有视频上传功能的新网站。视频保存到数据库，但上传后返回

no function clause matching in EngpinWeb.VideoController.persist_file/2

我正在使用 Elixir 1.11.2和 Phoenix v1.5.7这是我的 Controller 中的代码，它说正在返回错误。

 defp persist_file(video, %{path: temp_path}) do
   video_path = build_video_path(video)
    unless File.exists?(video_path) do
     video_path |> Path.dirname() |> File.mkdir_p()
     File.copy!(temp_path, video_path)
    end

但是我一直找不到任何东西来处理这个持久性问题。
这是整个 Controller 的其余部分

defmodule EngpinWeb.VideoController do
  2   use EngpinWeb, :controller
  3 
  4   import PhoenixVideoStream.Util, only: [build_video_path: 1]
  5 
  6   alias Engpin.Teachers
  7   alias Engpin.Teachers.Video
  8 
  9 
 10   def index(conn, _params) do
 11     videos = Teachers.list_videos()
 12     render(conn, "index.html", videos: videos)
 13   end
 14 
 15   def new(conn, _params) do
 16     changeset = Teachers.change_video(%Video{})
 17     render(conn, "new.html", changeset: changeset)
 18   end
 19 
 20   def create(conn, %{"video" => video_params}) do
 21     IO.inspect video_params
 22   changeset = Video.changeset(%Video{}, video_params)
 23   case Teachers.create_video(video_params) do
 24     {:ok, video} ->
 25       persist_file(video, video_params["video_file_id"])
 26 
 27       conn
 28       |> put_flash(:info, "Video created successfully.")
 29       |> redirect(to: Routes.video_path(conn, :show, :video))
 30     {:error, changeset} ->
 31       render(conn, "new.html", changeset: changeset)
 32     end
 33   end
 34 #def create(conn, %{"video" => video_params}) do
 35     #  case Teachers.create_video(video_params) do
 36     #    {:ok, video} ->
 37     #      conn
 38    #      |> put_flash(:info, "Video created successfully.")
 39    #      |> redirect(to: Routes.video_path(conn, :show, video))
 40   
 41     #    {:error, %Ecto.Changeset{} = changeset} ->
 42    #      render(conn, "new.html", changeset: changeset)
 43    #  end
 44   #end
 45 
 46   def show(conn, %{"id" => id}) do
 47     video = Teachers.get_video!(id)
 48     render(conn, "show.html", video: video)
 49   end
 50 
 51   def edit(conn, %{"id" => id}) do
 52     video = Teachers.get_video!(id)
 53     changeset = Teachers.change_video(video)
 54     render(conn, "edit.html", video: video, changeset: changeset)
 55   end
 56 
 57   def update(conn, %{"id" => id, "video" => video_params}) do
 58     video = Teachers.get_video!(id)
 59 
 60     case Teachers.update_video(video, video_params) do
 61       {:ok, video} ->
 62         conn
 63         |> put_flash(:info, "Video updated successfully.")
 64         |> redirect(to: Routes.video_path(conn, :show, video))
 65 
 66       {:error, %Ecto.Changeset{} = changeset} ->
 67         render(conn, "edit.html", video: video, changeset: changeset)
 68     end
 69   end
 70 
 71   def delete(conn, %{"id" => id}) do
 72     video = Teachers.get_video!(id)
 73     {:ok, _video} = Teachers.delete_video(video)
 74 
 75     conn
 76     |> put_flash(:info, "Video deleted successfully.")
 77     |> redirect(to: Routes.video_path(conn, :index))
 78   end
 79 
 80   defp persist_file(video, %{path: temp_path}) do
 81    video_path = build_video_path(video)
 82     unless File.exists?(video_path) do
 83      video_path |> Path.dirname() |> File.mkdir_p()
 84      File.copy!(temp_path, video_path)
 85     end
 86   end
 87 end

Answer 1

如果您的函数 defp persist_file(video, %{path: temp_path})没有用于调用它的参数的匹配子句，然后找到该函数的调用站点并查看传入的实际参数。在这种情况下，我认为发生的情况是第二个参数是一个带有字符串键而不是符号，因此它与函数定义中的路径模式不匹配。
下面是一个例子:

iex(1)> %{foo: :bar} = %{:foo => :bar} 
%{foo: :bar}
iex(2)> %{foo: :bar} = %{"foo" => :bar}
** (MatchError) no match of right hand side value: %{"foo" => :bar}

在您的 persist_file 的具体情况下功能，试试这样:

defp persist_file(video, %{"path" => temp_path}) do
  video_path = build_video_path(video)
  unless File.exists?(video_path) do
    video_path |> Path.dirname() |> File.mkdir_p()
    File.copy!(temp_path, video_path)
  end
end

注意 map 模式有字符串键，就像 def create 中的 map 模式一样。从您的第 20 行开始。