Phoenix / Ecto Changeset带来的麻烦

Question

我在使用Ecto Changeset时遇到了很糟糕的情况。我只想创建一个带有“空”Changeset的新表单。命中控制器并调用Session.changeset(%Session{})行。然后它会命中Site.Session.changeset。在这里，cast调用失败，并显示以下错误。下面是完整的堆栈跟踪。灵丹妙药1.4，雨伞应用程序。

控制器：

defmodule Site.SessionController do
  use Site.Web, :controller
  alias Site.Session

  def login_form(conn, _params) do
    changeset = Session.changeset(%Session{})
    conn |> render "login_form.html", changeset: changeset
  end
end

该模块：

defmodule Site.Session do
  import Ecto.Changeset

  defstruct [:email, :password]

  @required_fields ~w(email password)
  @optional_fields ~w()

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, @required_fields ++ @optional_fields)
  end
end

错误：

function Site.Session.__changeset__/0 is undefined or private. Did you mean one of:
      * changeset/1
      * changeset/2

堆栈跟踪：

Request: GET /login
** (exit) an exception was raised:
    ** (UndefinedFunctionError) function Site.Session.__changeset__/0 is undefined or private. Did you mean one of:

      * changeset/1
      * changeset/2

        (site) Site.Session.__changeset__()
        (ecto) lib/ecto/changeset.ex:422: Ecto.Changeset.do_cast/4
        (site) web/controllers/session_controller.ex:9: Site.SessionController.login_form/2
        (site) web/controllers/session_controller.ex:3: Site.SessionController.action/2
        (site) web/controllers/session_controller.ex:3: Site.SessionController.phoenix_controller_pipeline/2
        (site) lib/site/endpoint.ex:1: Site.Endpoint.instrument/4
        (site) lib/phoenix/router.ex:261: Site.Router.dispatch/2
        (site) web/router.ex:1: Site.Router.do_call/2
        (site) lib/site/endpoint.ex:1: Site.Endpoint.phoenix_pipeline/1
        (site) lib/plug/debugger.ex:123: Site.Endpoint."call (overridable 3)"/2
        (site) lib/site/endpoint.ex:1: Site.Endpoint.call/2
        (plug) lib/plug/adapters/cowboy/handler.ex:15: Plug.Adapters.Cowboy.Handler.upgrade/4
        (cowboy) 

Answer 1

Dogbert上面的评论是正确的。我错过了这个模式。我认为它不会持久化，并且我在模块中有一个defstruct，但是遗憾的是:孩子们，不要忘记模式。

defmodule Site.Session do
  use Ecto.Schema
  import Ecto.Changeset

  @required_fields ~w(email password)
  @optional_fields ~w()

  schema "sessions" do
    field :email, :string
    field :password, :string
  end

  @doc """
  Builds a changeset based on the `struct` and `params`.
  """
  def changeset(struct, params \\ %{}) do
    struct
    |> cast(params, @required_fields ++ @optional_fields)
  end
end