Marten DU support using hierarchical schema support

README.md

run dotnet run with a local database 'foo' created + plv8 installed.

Program.fs

module dutest

open Marten
open Npgsql
open System
open System.Reflection
open Marten

type Case1 = { id: Guid; thing: int; status: bool }
type Case2 = { id: Guid; butts: string; ``where``: DateTime }

type DU = 
| Case1 of Case1
| Case2 of Case2
with member x.Id = 
        match x with 
        | Case1 c -> c.id 
        | Case2 c -> c.id

let connstring = "Host=localhost;Database=foo;UserName=postgres;Password=postgres"

let case1Guid = Guid.Parse "378dfc1f-98a7-4de3-a022-a4835ce9fbe7"
let case2Guid = Guid.Parse "716e9e89-cae3-4603-ac0e-080c90136737"

[<EntryPoint>]
let main _argv = 
    let store = DocumentStore.For(fun store -> 
        store.Connection(connstring)
        let duTy = typeof<DU>
        // have to filter out the auto-generated `Tags` static class.
        let innerTys = duTy.GetNestedTypes() |> Array.filter (fun t -> t.BaseType = duTy) |> Array.map MappedType.op_Implicit
        let mapping = store.Schema.For<DU>()
        mapping.AddSubClassHierarchy(innerTys) |> ignore
        ()
    )
    store.Schema.ApplyAllConfiguredChangesToDatabase ()
    use session = store.LightweightSession()
    
    session.Store(Case1 { id = case1Guid; thing = 10; status = true})
    session.Store(Case2 { id = case2Guid; butts = "lol"; ``where`` = DateTime.UtcNow })
    session.SaveChanges ()

    // the problem is that this works already with Marten.
    // we can't name the inner sealed classes of DU.Case1 or DU.Case2, which is the premise of the Marten support for hierarchical support (ie gimme all of these subclass instances) 
    let one = session.Load<DU>(case1Guid)
    let two = session.Load<DU>(case2Guid)
    
    printfn "%A" [one; two]
    0

test.fsproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.0</TargetFramework>
  </PropertyGroup>

  <ItemGroup>
    <Compile Include="Program.fs" />
  </ItemGroup>

  <ItemGroup>
    <PackageReference Include="Marten" Version="2.8.2" />
  </ItemGroup>
</Project>