Simplest example of a nested record update. Only one layer deep, and one way to update.

simpleNestedRecordUpdate.elm

module Main exposing (..)

import Html exposing (Html, div, section, button, text)
import Html.Attributes exposing ()
import Html.Events exposing (onClick)
import Browser exposing (sandbox)



-- Type Schemas
type alias NestedRecord =
    { name : String, timesClicked : Int }

type alias Model =
    { person : NestedRecord }
    


-- Model Initialization
init : Model
init = 
    { person = { name = "Iam You", timesClicked = 0 } }



-- VIEW
view : Model -> Html Msg
view model =
    div []
        [ section [] [ text ("My name is " ++ model.person.name) ]
        , section [] [ text ("You've clicked me " ++ String.fromInt model.person.timesClicked ++ " times") ]
        , button [ onClick Click ] [ text "Click Me" ]
        ]



-- UPDATE
type Msg
    = Click

update : Msg -> Model -> Model
update msg model =
    case msg of
        Click ->
            model
                |> updateNestedValue



-- Helper functions to update our nested record
updateModel : (NestedRecord -> NestedRecord) -> Model -> Model
updateModel updateFunction model =
    { model | person = updateFunction model.person }

setNestedValue : NestedRecord -> NestedRecord
setNestedValue nestedRecord =
    { nestedRecord | timesClicked = nestedRecord.timesClicked + 1 }

updateNestedValue : Model -> Model
updateNestedValue =
        updateModel <| setNestedValue



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