CODEWITHSUNDEEP
asp.net-coref#asp.net-core-webapiunion-typessystem.text.json
JakobFerdinand
JakobFerdinand

Reputation: 1449

How to serialize F# discriminated union types in F# Asp Core Wep API

I´m trying to build a F# Asp.Net Core 3.0 Web API where I send some F# records. As far as I know Asp.Net Core 3.0 uses System.Text.Json by default to serailize objects to json. To make the domain model self documenting I use F# Discriminated Union Types.

The model looks like that:

type Starttime =
    | NotStarted
    | Started of DateTime

type Category = {
    Name: string
    Starttime: Starttime
}

type ValueId = ValueId of String

type Value = {
    Id: ValueId
    Category: Category
}

So I have one union type with just one possibility ValueId and I have one union type with two possibilities Starttime with NotStarted and Started which contains a DateTime object.

Now in my controller I build some sample data and return that.

let isStarted i : Starttime =
    if i % 2 = 0 then
        Started DateTime.Now
    else
        NotStarted

[<HttpGet>]
member __.Get() : Value[] = 
    [|
        for index in 1..2 ->
            { 
                Id = ValueId (Guid.NewGuid().ToString())
                Category = {
                    Name = sprintf "Category %i" index
                    Starttime = isStarted index }
            }
    |]

When i look at the data returned in json I get the data for the single option union type (the Guid) but I never get a value for the multi option union type.

[
  {
    "id": {
      "tag": 0,
      "item": "6ed07303-6dfa-42b4-88ae-391bbebf772a"
    },
    "category": {
      "name": "Category 1",
      "starttime": {
        "tag": 0,
        "isNotStarted": true,
        "isStarted": false
      }
    }
  },
  {
    "id": {
      "tag": 0,
      "item": "5e122579-4945-4f19-919c-ad4cf16ad0ed"
    },
    "category": {
      "name": "Category 2",
      "starttime": {
        "tag": 1,
        "isNotStarted": false,
        "isStarted": true
      }
    }
  }
]

Does anyone know how to also send the values for the multi value union type? Or is it generally better to map discriminated union types to anonymous records?

Thank you!

Upvotes: 3

Views: 2117

Answers (1)

nilekirk
nilekirk

Reputation: 2383

At the moment, System.Text.Json does not support F# types (there's an open issue about this here)

For now, you can use this library instead.

Upvotes: 1

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