如何在 Elm 中使用需要有效负载的消息创建任务？

Question

对于不准确的问题标题感到抱歉。无法准确指出所讨论的问题。

我正在尝试使用 Alex Lew 在这个很棒的博客 post 中提到的 "translator pattern"：The Translator Pattern: a model for Child-to-Parent Communication in Elm。

但作为一个完全的 Elm 新手，在以下情况下我不太明白：

我有一个这样的模块（child 模式中的组件）：

module Pages.SignUp.Update exposing (update, Msg(..))
import Http
import HttpBuilder exposing (withHeader, withJsonBody, stringReader, jsonReader, send)
import Task exposing (Task)
import Json.Decode exposing (Decoder, bool, (:=))
import Json.Encode exposing (encode, object, string)
import String
import Update.Extra exposing (andThen)
import Debug


type alias Model =
    { displayName : String
    , displayNameErrors : List (Maybe String)
    , email : String
    , emailErrors : List  (Maybe String)
    , password : String
    , passwordConfirmation : String
    , passwordErrors : List (Maybe String)
    , modelValid : Bool
    , emailValidationPending : Bool
    , registrationPending : Bool }


emptyModel :  Model
emptyModel =
    { displayName = ""
    , displayNameErrors = []
    , email = ""
    , emailErrors = []
    , password = ""
    , passwordConfirmation = ""
    , passwordErrors = []
    , modelValid = False
    , emailValidationPending = False
    , registrationPending = False }

type InternalMsg
    = SetEmail String
    | SetDisplayName String
    | SetPassword String
    | SetPasswordConfirm String
    | Register
    | RegisterSucceed (HttpBuilder.Response Bool)
    | RegisterFail (HttpBuilder.Error String)
    | ValidateModel
    | Noop

type OutMsg 
    = UserRegistered

type Msg 
    = ForSelf InternalMsg
    | ForParent OutMsg

type alias TranslationDictionary msg =
    { onInternalMessage: InternalMsg -> msg
    , onUserRegistered: msg
    }

type alias Translator msg =
    Msg -> msg


translator : TranslationDictionary msg -> Translator msg
translator { onInternalMessage, onUserRegistered } msg =
    case msg of
        ForSelf internal ->
            onInternalMessage internal
        ForParent UserRegistered ->
            onUserRegistered 

never : Never -> a
never n =
    never n

generateParentMessage : OutMsg -> Cmd Msg
generateParentMessage outMsg =
    Task.perform never ForParent (Task.succeed outMsg )

init : ( Model, List Notification )
init =
    ( emptyModel, [] )

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

update  msg model =
    case Debug.log "Signup action" msg of
        SetEmail emailStr ->
            let model' =
                {model | email = emailStr }
            in
                 update ValidateModel model'

        SetDisplayName nameStr ->
            let model' = 
                { model | displayName = nameStr }
            in
                update ValidateModel model'

        SetPassword passwordStr ->
            let model' =
                { model | password = passwordStr }
            in
                update ValidateModel model'

        SetPasswordConfirm passwordConfirmStr ->
        let model' = 
            { model | passwordConfirmation = passwordConfirmStr }
        in 
            update ValidateModel model'

        ValidateModel ->
            let validatedModel =
                    validateModel model
                test = Debug.log "validated model" validatedModel
            in
                ( validatedModel, Cmd.none )

        Register ->
            ( { model | registrationPending = True }, registerUser model)

        RegisterSucceed _ -> 
            ( { model | registrationPending = False }, (generateParentMessage UserRegistered) )

        RegisterFail  error ->
            case  error of
                HttpBuilder.BadResponse response ->
                    case Debug.log "Register response status" response.status of
                        422 -> 
                            ( { model | registrationPending = False }, Cmd.none )
                        _ ->
                            ( { model | registrationPending = False }, Cmd.none )
                _ ->
                    ( { model | registrationPending = False }, Cmd.none)
        Noop ->
            (model, Cmd.none)


registerUser : Model -> Cmd Msg
registerUser model =
    let url = 
            "/api/users"

        user =
            object [
                ("user",
                    object
                    [
                        ("display_name", (string model.displayName)),
                        ("email", (string model.email)),
                        ("password", (string model.password)),
                        ("passwordConfirmation", (string model.passwordConfirmation))
                    ]
                )
            ]

        postRequest =
            HttpBuilder.post url
            |> withHeader "Content-type" "application/json"
            |> withJsonBody user
            |> send (jsonReader decodeRegisterResponse) stringReader
    in
        Task.perform ForSelf RegisterFail  ForSelf RegisterSucceed postRequest 

decodeRegisterResponse : Decoder Bool
decodeRegisterResponse = 
        "ok" := bool

validateRequired : String -> String -> Maybe String

validateRequired fieldContent fieldName =
            case String.isEmpty fieldContent of 
                True -> Just <| String.join " " [ fieldName, "required" ]
                False ->  Nothing

validateEmail : String -> List (Maybe String)

validateEmail email =
    let requiredResult = 
            validateRequired email "Email"
    in
        [requiredResult]

validatePassword : String -> String -> List (Maybe String) 
validatePassword password passwordConf =
    let requiredResult =
             validateRequired password "Password"
        confirmResult =
            case password == passwordConf of
                True -> Nothing
                False ->  Just "Password confirmation does not match"
    in
        [ requiredResult, confirmResult ] 

validateModel : Model -> Model
validateModel model =
    let emailResult =
            validateEmail model.email
        displayNameResult =
            validateRequired model.displayName "Displayname" :: []
        passwordResult =
            validatePassword model.password model.passwordConfirmation
        errors =
            List.concat [emailResult,  displayNameResult, passwordResult ] |> List.filterMap identity
        modelValid = List.isEmpty errors
    in
        { model | 
            emailErrors = emailResult,
            displayNameErrors = displayNameResult,
            passwordErrors = passwordResult,
            modelValid = modelValid
        }

问题出在 registerUser 函数上，它显然不能像现在这样工作。我无法将其发送至 return Cmd Msg。我可以这样 return Cmd InternalMsg 但是当然我运行会在更新功能注册消息时遇到问题。在那里我需要将 Cmd InternalMsg 转换为 Cmd Msg.

我已经尝试在这两个地方解决这个问题，但总是失败。很可能有一个简单的解决方案，但遗憾的是，似乎没有技能可以做到这一点。

如有任何帮助，我们将不胜感激。

Answer 1

这是翻译器模式的丑陋部分，您应该 Cmd.map 您对 Msg 消息的命令，而不是：

Task.perform ForSelf RegisterFail  ForSelf RegisterSucceed postRequest

你应该有这样的东西：

Cmd.map ForSelf (Task.perform RegisterFail RegisterSucceed postRequest)

如何在 Elm 中使用需要有效负载的消息创建任务？

How to create a Task with messages that require payload in Elm?

elm