通过动态字段名称更新字段

Question

我想使用动态字段名称来更新字段。在我的示例中，我有两个div和contenteditable属性。在blur事件中，我需要更新模型（每个div更新其字段）。

module UpdateTest exposing (main)

import Browser
import Html exposing (..)
import Html.Attributes exposing (..)
import Html.Events exposing (on)
import Json.Decode as Json
import Debug

type alias Model =
    { field1 : String
    , field2 : String
    }

type Msg = Update String String

main : Program () Model Msg
main =
    Browser.element
        { init = init
        , subscriptions = subscriptions
        , view = view
        , update = update
        }

init : () -> ( Model, Cmd Msg )
init () =
    ( { field1 = "value 1", field2 = "value2" }, Cmd.none )

subscriptions : Model -> Sub Msg
subscriptions model =
    Sub.none

view : Model -> Html Msg
view model =
    div []
        [ div [ contenteditable True, attribute "data-id" "field1", onBlur (Update "field1") ] [ text model.field1 ]
        , div [ contenteditable True, attribute "data-id" "field2", onBlur (Update "field2") ] [ text model.field2 ]
        , div [ id "fiedl11" ] [ text model.field1 ]
        , div [ id "fiedl12" ] [ text model.field2 ]
        ]

onBlur : (String -> msg) -> Attribute msg
onBlur tagger =
    on "blur" (Json.map tagger targetTextContent) 

targetTextContent : Json.Decoder String
targetTextContent =
  Json.at ["target", "textContent"] Json.string

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        Update id text ->
            ({model | id = Debug.log id text }, Cmd.none) -- here the issue

你认为有更好的东西吗？

Answer 1

Elm是一种静态类型的语言，因此无法使用字符串值来引用记录的字段，因为这会导致在运行时发生类型错误。

Elm还缺少任何类型的运行时自省/反射，因此您无法在运行时获取类型信息，该信息会使您自动将字符串与记录的字段名称进行匹配。

您将需要执行以下操作：

update : Msg -> Model -> ( Model, Cmd Msg )
update msg model =
    case msg of
        Update id text -> case id of
            "field1" -> ({model | field1 = text }, Cmd.none)
            "field2" -> ({model | field2 = text }, Cmd.none)