从榆树模型中删除值答案

【问题标题】：deleting values from elm model从榆树模型中删除值
【发布时间】：2018-05-30 11:43:55
【问题描述】：

我已经成功实现了elm tutorial 的删除播放器方法。但是，如果不手动发送 ForchFetch 消息（通过单击按钮）再次从服务器获取玩家，我无法更新模型。这是我的代码：

我的删除按钮：

deleteBtn : Player -> Html.Html Msg
deleteBtn player =
    let
        message =
            Msgs.Delete player
    in
       a
            [ class "btn regular", onClick message]
            [ i [ class "fa fa-pencil mr1" ] [], text "Delete" ]

我的删除消息：

type Msg = 
    | Delete Player
    | OnDeletePlayer (Result Http.Error Player) 
    | ForceFetch
    | OnFetchPlayers (WebData (List Player))

我的更新功能：

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
        Msgs.ForceFetch ->
          (model, fetchPlayers)
        Msgs.OnFetchPlayers response -> 
        ( { model | players = response }, Cmd.none )
        Msgs.Delete player ->
          (model, deletePlayerCmd player)

        Msgs.OnDeletePlayer (Ok player) ->
          (updateDeletedPlayerList model player, Cmd.none)

        Msgs.OnDeletePlayer (Err player) ->
          (model, Cmd.none)

updateDeletedPlayerList : Model -> Player -> Model 
updateDeletedPlayerList model deletedPlayer =     
     let
         updatedPlayers = RemoteData.map (List.filter (\p -> deletedPlayer /= p)) model.players
     in
         { model | players = updatedPlayers}

deletePlayerCmd : Player -> Cmd Msg
deletePlayerCmd player =
      Http.send Msgs.OnDeletePlayer (deletePlayerRequest player)

deletePlayerRequest : Player -> Http.Request Player
deletePlayerRequest player =
 Http.request
        { body = Http.emptyBody
        , expect = Http.expectJson playerDecoder
        , headers = []
        , method = "DELETE"
        , timeout = Nothing
        , url = savePlayerUrl player.id
        , withCredentials = False
        }
fetchPlayers : Cmd Msg
fetchPlayers =
    Http.get fetchPlayersUrl playersDecoder 
        |> RemoteData.sendRequest 
        |> Cmd.map Msgs.OnFetchPlayers

为了更好地衡量我的模型：

type alias Model =
    { players : WebData (List Player)
    , route : Route
    , newPlayerName : String
    , newPlayerId : String
    , newPlayerLevel : Int
    }

编辑：

我尝试以以下方式合并fetchPlayers，但没有成功：

Msgs.OnDeletePlayer (Ok player) ->
          (updateDeletedPlayerList model player, fetchPlayers)

【问题讨论】：

如果ForceFetch 有效，我不明白为什么您的编辑尝试无效。您确定回复最终是Ok 而不是Err？
我解决了，我会尽快更新答案。
如果您在过滤器中比较玩家记录，它们可能不匹配，因为您从服务器获得的记录可能不同。最好只对 player.id 进行比较。

标签： functional-programming single-page-application elm

【解决方案1】：

如果您不想在删除后获取模型，则需要更新代码中的模型，因此您有：

Msgs.Delete player ->
          (model, deletePlayerCmd player)

您需要将“模型”更改为可以从中移除播放器的函数：

    Msgs.Delete player ->
        (removePlayer player model, deletePlayerCmd player)

...
removePlayer : Player -> Model -> Model
...

【讨论】：