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How to do complex validation with piglets (e.g. Check password = password confirmation)
websharperpigletsvalidation

A common scenario for validation is the need to check some condition over multiple fields. For example checking that two passwords entered on a signup form are equal.

I've tried to do this using MapToResult but I'm not getting the behaviour I was hoping for. I don't want the errors displayed until the submit button is clicked but (validatedPw.Through submit) does not seem to be delaying the errors. I also want to limit the errors displayed next to the password confirmation box to the 'passwords don't match' error but instead I am getting all of the errors from the complete piglet.

This is what I have:

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namespace Application2

open WebSharper
open WebSharper.JavaScript
open WebSharper.Html.Client

open WebSharper.Piglets

[<JavaScript>]
module Client =

    let registerPiglet =
      Piglet.Return (fun username pw1 pw2 -> (username, pw1, pw2))
        <*>
          (Piglet.Yield ""
          |> Piglet.Validation.Is Piglet.Validation.NotEmpty "Must be non-empty")
        <*>
          (Piglet.Yield ""
          |> Piglet.Validation.Is Piglet.Validation.NotEmpty "Must be non-empty")
        <*>
          (Piglet.Yield ""
          |> Piglet.Validation.Is Piglet.Validation.NotEmpty "Must be non-empty")
      |> Piglet.MapToResult (fun (username, pw1, pw2) ->
        if pw1 <> pw2 then Piglets.Result.Failwith "Password must match" else Piglets.Result.Success((username, pw1))
        )
      |> Piglet.TransmitReader
      |> Piglet.WithSubmit
      |> Piglet.Run (fun (username, password) ->
        WebSharper.JavaScript.Console.Log (username + "," + password))

    let renderPiglet() =
      registerPiglet
      |> Piglet.Render (fun username pw1 pw2 validatedPw submit ->
        Div [
          Div [
            Label [
              Text "Username"
              Controls.Input username :> Pagelet
              Span [Attr.Class "color:red"]
              |> Controls.ShowErrors (username.Through submit)
                  (fun errors -> List.map Text errors) :> Pagelet
            ]
          ]
          Div [
            Label [
              Text "Password"
              Controls.Input pw1 :> Pagelet
              Span [Attr.Class "color:red"]
              |> Controls.ShowErrors (pw1.Through submit)
                  (fun errors -> List.map Text errors) :> Pagelet
            ]
          ]
          Div [
            Label [
              Text "Confirm Password"
              Controls.Input pw2 :> Pagelet
              Span [Attr.Class "color:red"]
              |> Controls.ShowErrors (validatedPw.Through submit)
                  (fun errors -> List.map Text errors) :> Pagelet
            ]
          ]
          Div [
            Controls.Submit submit
          ]          
      ])



    let Main () =
        Div [
          renderPiglet()
        ]
.

I'm still not very well-versed in Piglets but I'm not sure this can be solved nicely. Basically the problem here is that you want to put validation on a field that depends on a previous one, but on the field you want to access the previous one you only have access to the value of that particular one. If you decide to instead do the validation on the whole Piglet where you have both values you can obviously do it but when you pass on the reader you will receive all errors from that Piglet.

With that said, here's a rather clumsy but working solution (maybe Loïc can chip in on this later):

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module V = Piglet.Validation

let notEmpty p = V.Is V.NotEmpty "Must be non-empty" p

let pwFields =
    let s = new Stream<string>(Result.Success "")

    Piglet.Return (fun pw1 pw2 -> (pw1, pw2))
    // create the Piglet from a stream whose Id we know in advance
    <*> (Piglet.Create s (fun f -> f s) |> notEmpty) 
    <*> Piglet.Yield ""
    |> V.Is (fun (pw1, pw2) -> pw1 = pw2) "Passwords must match."
    |> Piglet.Map fst
    |> Piglet.TransmitReaderMapResult (function
        | Success s -> Success s
        // only propagate errors that are from the right stream
        | Failure f -> f |> List.filter (fun e -> e.Source <> s.Id) |> Failure)

let registerPiglet =
    Piglet.Return (fun username pw -> (username, pw))
    <*> (Piglet.Yield "" |> notEmpty)
    <*> pwFields
    |> Piglet.WithSubmit
    |> Piglet.Run (fun (username, pw) ->
        WebSharper.JavaScript.Console.Log (username + "," + pw))

let renderPiglet () =
  registerPiglet
  |> Piglet.Render (fun username pw1 pw2 matchingPw submit ->
        let mkControl lbl s (es : Reader<string>) =
            Div [
                Label [ Text lbl ] -< [
                    Controls.Input s
                    Span [Attr.Style "color:red"]
                    |> Controls.ShowErrors (es.Through submit)
                        (fun errors -> List.map Text errors)
                ]
            ]
        Div [
            mkControl "Username" username username
            mkControl "Password" pw1 pw1
            mkControl "Confirm password" pw2 matchingPw
            Div [ Controls.Submit submit ]
        ])
By on 7/16/2015 1:58 AM ()

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