Maybe 错误和 Elm 中的嵌套资源

Question

我正在构建我的第一个 Elm SPA，我正在不同的文件夹和模块中组织我的组件。一切正常，直到我从这里更改主模型：

type alias Model =
{ contacts : Contacts.Model.Model
, contact : Contact.Model.Model
, route : Routing.Route
}

为此：

type alias Model =
{ contacts : Contacts.Model.Model
, contact : Maybe Contact.Model.Model
, route : Routing.Route
}

我已经在代码库中进行了所有必要的更改以使其正常工作，但我遗漏了一些我找不到的东西，因为在 Update 主模块中我经常遇到此编译错误:

The type annotation for `update` does not match its definition. - The type annotation is saying:

    Msg
    -> { ..., contact : Maybe Contact.Model.Model }
    -> ( { contact : Maybe Contact.Model.Model
    , contacts : Contacts.Model.Model
    , route : Routing.Route
    }
    , Cmd Msg
    )

But I am inferring that the definition has this type:

    Msg
    -> { ...
    , contact :
          { birth_date : String
          , email : String
          , first_name : String
          , gender : Int
          , headline : String
          , id : Int
          , last_name : String
          , location : String
          , phone_number : String
          , picture : String
          }
    }
    -> ( { contact : Maybe Contact.Model.Model
    , contacts : Contacts.Model.Model
    , route : Routing.Route
    }
    , Cmd Msg
    )

我好像错过了在某处传递 Maybe Model 但我找不到它。这是更新功能的样子：

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
case msg of
    ContactsMsg subMsg ->
        let
            ( updatedContacts, cmd ) =
                Contacts.Update.update subMsg model.contacts
        in
            ( { model | contacts = updatedContacts, contact = Nothing }, Cmd.map ContactsMsg cmd )

    ContactMsg subMsg ->
        let
            ( updatedContact, cmd ) =
                Contact.Update.update subMsg model.contact
        in
            ( { model | contact = updatedContact }, Cmd.map ContactMsg cmd )

这是完整的回购协议，有错误：https://github.com/bigardone/phoenix-and-elm/tree/feature/routes-refactoring/web/elm

我做错了什么？非常感谢您！

Answer 1

问题是由 Update.update 函数中的类型不匹配引起的。

update : Msg -> Model -> ( Model, Cmd Msg )

您必须处理 Update.elm 中的 Maybe 值：

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        ContactsMsg subMsg ->
            let
                ( updatedContacts, cmd ) =
                    Contacts.Update.update subMsg model.contacts
            in
                ( { model | contacts = updatedContacts, contact = Nothing }
                , Cmd.map ContactsMsg cmd
                )

        ContactMsg subMsg ->
            case model.contact of
                Just contact ->
                    let
                        ( updatedContact, cmd ) =
                            Contact.Update.update subMsg contact
                    in
                        ( { model | contact = updatedContact }
                        , Cmd.map ContactMsg cmd
                        )

                Nothing ->
                    ( model, Cmd.none )

Maybe 错误和 Elm 中的嵌套资源

Error with Maybe and nested resources in Elm

elm