I have a C# Asp.Net MVC (5.2.7) app with support for WebApi 2.x targeting .Net 4.5.1. I am experimenting with F# and I added an F# library project to the solution. The web app references the F# library.
Now, I want to be able to have the C# WebApi controller return F# objects and also save F# objects. I have trouble serializing a F# record with an Option field. Here is the code:
C# WebApi controller:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using FsLib;
namespace TestWebApp.Controllers
{
[Route("api/v1/Test")]
public class TestController : ApiController
{
// GET api/<controller>
public IHttpActionResult Get()
{
return Json(Test.getPersons);
}
// GET api/<controller>/5
public string Get(int id)
{
return "value";
}
[AllowAnonymous]
// POST api/<controller>
public IHttpActionResult Post([FromBody] Test.Person value)
{
return Json(Test.doSomethingCrazy(value));
}
// PUT api/<controller>/5
public void Put(int id, [FromBody]string value)
{
}
// DELETE api/<controller>/5
public void Delete(int id)
{
}
}
}
FsLib.fs:
namespace FsLib
open System.Web.Mvc
open Option
open Newtonsoft.Json
module Test =
[<CLIMutable>]
//[<JsonConverter(typeof<Newtonsoft.Json.Converters.IdiomaticDuConverter>)>]
type Person = {
Name: string;
Age: int;
[<JsonConverter(typeof<Newtonsoft.Json.FSharp.OptionConverter>)>]
Children: Option<int> }
let getPersons = [{Name="Scorpion King";Age=30; Children = Some 3} ; {Name = "Popeye"; Age = 40; Children = None}] |> List.toSeq
let doSomethingCrazy (person: Person) = {
Name = person.Name.ToUpper();
Age = person.Age + 2 ;
Children = if person.Children.IsNone then Some 1 else person.Children |> Option.map (fun v -> v + 1); }
let deserializePerson (str:string) = JsonConvert.DeserializeObject<Person>(str)
Here is the OptionConverter:
namespace Newtonsoft.Json.FSharp
open System
open System.Collections.Generic
open Microsoft.FSharp.Reflection
open Newtonsoft.Json
open Newtonsoft.Json.Converters
/// Converts F# Option values to JSON
type OptionConverter() =
inherit JsonConverter()
override x.CanConvert(t) =
t.IsGenericType && t.GetGenericTypeDefinition() = typedefof<option<_>>
override x.WriteJson(writer, value, serializer) =
let value =
if value = null then null
else
let _,fields = FSharpValue.GetUnionFields(value, value.GetType())
fields.[0]
serializer.Serialize(writer, value)
override x.ReadJson(reader, t, existingValue, serializer) =
let innerType = t.GetGenericArguments().[0]
let innerType =
if innerType.IsValueType then typedefof<Nullable<_>>.MakeGenericType([|innerType|])
else innerType
let value = serializer.Deserialize(reader, innerType)
let cases = FSharpType.GetUnionCases(t)
if value = null then FSharpValue.MakeUnion(cases.[0], [||])
else FSharpValue.MakeUnion(cases.[1], [|value|])
I want to serialize the Option field to the value, if it is not None and to null if it is None. And vice-versa, null -> None, value -> Some value.
The serialization works fine:
[
{
"Name": "Scorpion King",
"Age": 30,
"Children": 3
},
{
"Name": "Popeye",
"Age": 40,
"Children": null
}
]
However, when I post to the url, Person parameter is serialized to null and the ReadJson method is not invoked. I used Postman (the chrome app) to post by selecting the Body -> x-www-form-urlencoded. I set up three parameters: Name=Blob,Age=103,Children=2.
In WebApiConfig.cs I have:
config.Formatters.JsonFormatter.SerializerSettings.Converters.Add(new Newtonsoft.Json.FSharp.OptionConverter());
However, if I just have this and remove the JsonConverter attribute from the Children field, it doesn't seem to have any effect.
This what gets sent to the server:
POST /api/v1/Test HTTP/1.1
Host: localhost:8249
Content-Type: application/x-www-form-urlencoded
Cache-Control: no-cache
Postman-Token: b831e048-2317-2580-c62f-a00312e9103b
Name=Blob&Age=103&Children=2
So, I don't know what's wrong, why the deserializer converts the object to null. If I remove the option field it works fine. Also if I remove the Children field from the payload it works fine as well. I do not understand why the ReadJson method of the OptionCoverter is not invoked.
Any ideas?
Thanks
An update: In the comments it was rightly pointed I did not post a application/json payload. I did it and the serialization still doesn't work properly.
Update 2: After more testing, this works:
public IHttpActionResult Post(/*[FromBody]Test.Person value */)
{
HttpContent requestContent = Request.Content;
string jsonContent = requestContent.ReadAsStringAsync().Result;
var value = Test.deserializePerson(jsonContent);
return Json(Test.doSomethingCrazy(value));
}
The following is the Linqpad code I used for testing the request (I didn't use postman):
var baseAddress = "http://localhost:49286/api/v1/Test";
var http = (HttpWebRequest) WebRequest.Create(new Uri(baseAddress));
http.Accept = "application/json";
http.ContentType = "application/json";
http.Method = "POST";
string parsedContent = "{\"Name\":\"Blob\",\"Age\":100,\"Children\":2}";
ASCIIEncoding encoding = new ASCIIEncoding();
Byte[] bytes = encoding.GetBytes(parsedContent);
Stream newStream = http.GetRequestStream();
newStream.Write(bytes, 0, bytes.Length);
newStream.Close();
var response = http.GetResponse();
var stream = response.GetResponseStream();
var sr = new StreamReader(stream);
var content = sr.ReadToEnd();
content.Dump();
Update 3:
This works just fine - i.e. I used a C# class:
public IHttpActionResult Post(/*[FromBody]Test.Person*/ Person2 value)
{
// HttpContent requestContent = Request.Content;
// string jsonContent = requestContent.ReadAsStringAsync().Result;
//
// var value = Test.deserializePerson(jsonContent);
value.Children = value.Children.HasValue ? value.Children.Value + 1 : 1;
return Json(value);//Json(Test.doSomethingCrazy(value));
}
public class Person2
{
public string Name { get; set; }
public int Age { get; set; }
public int? Children { get; set; }
}
