json to object and object to json - json

Question

In context of this tutorial on F# snippets http://www.fssnip.net/1l/title/Convert-an-object-to-json-and-json-to-object
Let's say a Person type
type Person = {
entityName: string;
entityType: string;
}
and the code to call the web service and convert into json.
let internal json<'t> (myObj:'t) =
use ms = new MemoryStream()
(new DataContractJsonSerializer(typeof<'t>)).WriteObject(ms, myObj)
Encoding.Default.GetString(ms.ToArray())
let internal unjson<'t> (jsonString:string) : 't =
use ms = new MemoryStream(ASCIIEncoding.Default.GetBytes(jsonString))
let obj = (new DataContractJsonSerializer(typeof<'t>)).ReadObject(ms)
obj :?> 't
let requestToken (): Token =
let url = "http://example.com"
let request = WebRequest.Create(url) :?> HttpWebRequest
request.Method <- "POST"
request.Accept <- "application/json;charset=UTF-8"
let response = request.GetResponse() :?> HttpWebResponse
use reader = new StreamReader(response.GetResponseStream())
let body = reader.ReadToEnd()
Console.WriteLine body // result OK
let result = unjson<Person> body
JSON
{
"entityName": "john doe",
"entityType": "client"
}
Error
System.Runtime.Serialization.SerializationException: The data contract type 'Person' cannot be deserialized because the required data members 'entityName#, entityType#' were not found.
if someone can add an example on how to call 'json' function passing result object to convert the object back into the JSON string
Is the Person type required to have all fields as per JSON schema or can I choose to leave out non-required fields?

Answer 1

This will serialize your record to JSON using the DataContractSerializer. You need to add some attributes for this to work.
#r "System.Runtime.Serialization"
open System.IO
open System.Runtime.Serialization.Json
open System.Runtime.Serialization
[<DataContract>]
[<CLIMutable>]
type Person = {
[<DataMember(Name="Name") >]
entityName: string
[<DataMember(Name="Type") >]
entityType: string
}
let person = {entityName = "ENTITY"; entityType ="TYPE"}
let toJson<'t> (myObj:'t) =
let fs = new FileStream(#"C:\tmp\test.json",FileMode.Create)
(new DataContractJsonSerializer(typeof<'t>)).WriteObject(fs,myObj)
toJson<Person> person
And this is the output I get in the test.json file:
{"Name":"ENTITY","Type":"TYPE"}