open System
open System.Reflection
open MongoDB.Bson
open MongoDB.Bson.Serialization
open MongoDB.Bson.Serialization.Serializers
open MongoDB.Driver
open MongoDB.Driver.Core

type YourImmutableRecord = { id : Guid; text : string }

let ctor = (typeof<YourImmutableRecord >).GetConstructors().[0]

let map (a : BsonClassMap<YourImmutableRecord>) =
    a.AutoMap()
    a.MapIdMember(fun (a) -> a.id).SetSerializer(new GuidSerializer(BsonType.String)) |> ignore
    a.MapProperty(fun (a) -> a.text) |> ignore
    a.MapConstructor(ctor, ctor.GetParameters() |> Array.map (fun (a) -> a.Name)) |> ignore

let mapper = Action<_>(fun (a : BsonClassMap<YourImmutableRecord>) -> map a)

BsonClassMap.RegisterClassMap<YourImmutableRecord> mapper |> ignore