open System

open System.Linq

open System.Text

open System.Runtime.Serialization.Formatters

open System.IO

open System.Data

open System.ComponentModel.DataAnnotations

open System.Globalization

open System.Reflection

​

open Microsoft.FSharp.Reflection

​

open Newtonsoft.Json

open Newtonsoft.Json.Linq

open Newtonsoft.Json.Converters

open Newtonsoft.Json.Serialization

​

//https://stackoverflow.com/questions/73551490/how-to-define-singleorarrayconverter-to-handle-json-property-in-f-port-from-c

​

module JsonExtensions =

    type JsonReader with

        member r.ReadAndAssert() = 

            if not (r.Read()) then raise (JsonReaderException("Unexpected end of JSON stream."))

            r

        member r.MoveToContentAndAssert() =

            if r.TokenType = JsonToken.None then r.ReadAndAssert() |> ignore

            while r.TokenType = JsonToken.Comment do r.ReadAndAssert() |> ignore

            r

​

open JsonExtensions

​

type SingleOrArrayConverter<'T>() =

    inherit JsonConverter()

    override this.CanConvert(objectType) = objectType = typeof<ResizeArray<'T>> 

    override this.ReadJson(reader, objectType, existingValue, serializer) = 

        let a = if (existingValue :? ResizeArray<'T>) then existingValue :?> ResizeArray<'T> else ResizeArray<'T>() // Reuse the incoming List<T> if preallocated

        match reader.MoveToContentAndAssert().TokenType with

        | JsonToken.StartArray -> serializer.Populate(reader, a)

        | _ -> a.Add(serializer.Deserialize<'T>(reader))

        a :> obj

    override this.CanWrite = false                       // Simplified syntax

    override this.WriteJson(writer, value, serializer) = raise (new NotImplementedException())

type Locality = {

    category: string

    id: int

    location: string

    postcode: int

    state: string

    latitude: decimal

    longitude: decimal

}

​

type Localities = {

    [<JsonProperty("locality")>]

    [<JsonConverter(typeof<SingleOrArrayConverter<Locality>>)>]  // Fix syntax: typeof<'T> not typeof(T)

    locality: ResizeArray<Locality>

}

​

type PostCodeLocality = {

    localities : Localities

}

​

let json0 = """

{/* Some COmment */

  /* Some COmment */ "localities": { /* Some COmment */

    "locality":

      /* Some COmment */ /* Some COmment */ { /* Some COmment */

        "category": "category",

        "id": 101,

        "location": "location",

        "postcode": 22,

        "state": "ZZ",

        "latitude": 81.0,

        "longitude": 202.0

      }/* Some COmment */

  }/* Some COmment */

}/* Some COmment */

"""

​

let p1 = JsonConvert.DeserializeObject<PostCodeLocality>(json0)

​

let p2 : PostCodeLocality = { localities = { locality = new ResizeArray<Locality>([|{category="category"; id=101; location="location"; postcode=22;state="ZZ"; latitude=81.0M; longitude=202M }|]) } }

​

let json1 = JsonConvert.SerializeObject(p1, Formatting.Indented)

​

let json2 = JsonConvert.SerializeObject(p2, Formatting.Indented)

​

if (json1 <> json2) then raise (Exception("json1 != json2"))

​

let p3 = JsonConvert.DeserializeObject<PostCodeLocality>(json2)

​

let json3 = JsonConvert.SerializeObject(p3, Formatting.Indented)

​

if (json1 <> json3) then raise (Exception("json1 != json3"))

​

​