F# Try to parse nested JSON objects

Question

Hello,

I found a C# program to parse nested JSON object:

    protected void Page_Load(object sender, EventArgs e) 
    { 
 
        string jSon = 
            "{\"FirstName\":\"Foo\", " + 
            "\"LastName\":\"Bar\"," + 
            "\"Hobbies\":" + 
            "[" + 
                "{\"Sport\":\"FootBall\"},{\"Music\":\"Rock\"}" + 
            "]}"; 
        var serializer = new System.Web.Script.Serialization.JavaScriptSerializer(); 
        User user = serializer.Deserialize<User>(jSon); 
 
    } 
 
    public class User 
    { 
        public string FirstName { get; set; } 
        
        public string LastName { get; set; } 
        public System.Collections.ObjectModel.Collection<Hobbie> Hobbies { get; set; } 
 
    } 
 
    public class Hobbie 
    { 
        public string Sport { get; set; } 
        public string Music { get; set; } 
    }

I want to do the same in F#

open System.Collections.ObjectModel

open System.Runtime.Serialization

open System.Runtime.Serialization.Json

open System.Text

[<DataContract>]

type people() =

     let mutable firstName = ""

     let mutable lastName = ""

     [<DataMember>]

     member p.FirstName with get() = firstName and set(v) = firstName <- v

     [<DataMember>]

     member p.LastName with get() = lastName and set(v) = lastName <- v

However, I don’t know how to declare nested structure in F#.

Any one has any idea?

Besides, how to parse it using JSON in F#?

Thanks,

Answer 1

Usually you could define nested data structures using F# discriminated unions.

Take a look for example at this post: http://blog.efvincent.com/parsing-json-using-f

---

Petr

Answer 2

You can do it exactly like C#.  With F# 3.0:

let json = """
    { "FirstName":"Foo", 
      "LastName":"Bar",
      "Hobbies":
        [
            {"Sport":"FootBall"},{"Music":"Rock"}
        ]}   """
type Hobby() =
    member val Sport = "" with get, set
    member val Music = "" with get, set
    override this.ToString() = this.Sport + " " + this.Music
type User() =
    member val FirstName = "" with get, set
    member val LastName = "" with get, set
    member val Hobbies : System.Collections.ObjectModel.Collection<Hobby> = null with get, set
    override this.ToString() = 
        sprintf "%s, %s: %A" this.LastName this.FirstName (this.Hobbies |> Seq.toList)
// reference System.Web.Extensions.dll
let serializer = new System.Web.Script.Serialization.JavaScriptSerializer()
let user = serializer.Deserialize<User>(json)
printfn "%A" user

EDIT:

Actually, using records with the new F# 3.0 CLIMutableAttribute is an even easier way to describe the structure:

[<CLIMutable>]
type Hobby = { Sport:string; Music:string }
[<CLIMutable>]
type User = { FirstName:string; LastName:string; Hobbies : System.Collections.ObjectModel.Collection<Hobby> }

---

Brian McNamara [MSFT]

Answer 3

Hello,

Thank you very much, your code works.

And it is similar to C#!