使用 Newtonsoft.Json 在 F# 中反序列化私有类型

Question

When working with Newtonsoft.Json, how do you deserialize private types? For example:

[<CLIMuteable>]
type private Foo = {
  Bar:string
}

module Foo =
  let deserialize str=
      str |> Newtonsoft.Json.JsonCovert.DeserializeObject<Foo>

Answer 1

This sounds rather unusual, but I'll assume you have a good reason to use a private type.

The problem here is that Json.NET cannot see the any public properties on the type, you can fix this by using a custom contract resolver and tell it to find the private members.

Like this:

open System
open System.Reflection
open FSharp.Core
open Newtonsoft.Json
open Newtonsoft.Json.Serialization

[<CLIMutable>]
type private Foo = {
  Bar:string
}

type PrivateContractResolver() =
    inherit DefaultContractResolver()
    override this.GetSerializableMembers(objectType : Type) = 
        let flags = BindingFlags.Instance ||| BindingFlags.Public ||| BindingFlags.NonPublic
        let fields = objectType.GetFields (flags) |> Seq.cast<MemberInfo> |> Seq.toArray
        fields |> Array.append (objectType.GetProperties (flags) |> Array.filter (fun propInfo -> propInfo.CanWrite) |> Seq.cast<MemberInfo> |> Seq.toArray) |> ResizeArray
    override this.CreateProperties(t : Type, _ : MemberSerialization) = 
        base.CreateProperties (t, MemberSerialization.Fields)

module Foo =

  let deserialize str =
      let settings = JsonSerializerSettings()
      settings.ContractResolver <- PrivateContractResolver()
      let r = Newtonsoft.Json.JsonConvert.DeserializeObject<Foo>(str, settings)
      r.Bar

[<EntryPoint>]
let main _ =
    let result = Foo.deserialize """
{ 'Bar': 'Hi' }
"""
    printfn "%s" result
    0