Single Case Discriminated Unions as Identifiers

I am just playing around with the library and it works great so far. In the concrete use case I am considering to use it, however, we are using single case discriminated unions for ids quite heavily. The good news: Inserting records which use a DU as id works.

But I noticed that querying for a record that has just been inserted does not work. Also indexing isn’t working. Sample:

open System
open System.IO
open LiteDB
open LiteDB.FSharp

type FooId = FooId of Guid

type Foo = 
    { Id : FooId
      ParentId : FooId option }

[<EntryPoint>]
let main argv =
    let mapper = FSharpBsonMapper()
    let path = Path.Combine(Directory.GetCurrentDirectory(), "test.db")
    use db = new LiteDatabase(path, mapper)
    
    let id = Guid.NewGuid()
    
    let demoFoo =
      { Id = FooId(id)
        ParentId = None }
    
    let collection = db.GetCollection<Foo>()
    
    collection.Insert(demoFoo) |> ignore
    let indexEnsured = collection.EnsureIndex(fun x -> x.Id)
    printfn "Index ensured: %b" indexEnsured
    
    let allFoos = collection.FindAll() |> Seq.toList
    printfn "Total: %i" allFoos.Length
    
    let result = collection.FindById(BsonValue(id))
    printfn "Last one: %s" (result.Id.ToString())
    0

collection.FindById(BsonValue(id)) will just return null, indexEnsured is false.

When removing the DU and using theGuid directly, everything works as expected.

open System
open System.IO
open LiteDB
open LiteDB.FSharp

type FooId = FooId of Guid

type Foo = 
    { Id : Guid
      ParentId : FooId option }

[<EntryPoint>]
let main argv =
    let mapper = FSharpBsonMapper()
    let path = Path.Combine(Directory.GetCurrentDirectory(), "test.db")
    use db = new LiteDatabase(path, mapper)
    
    let id = Guid.NewGuid()
    
    let demoFoo =
      { Id = id
        ParentId = None }
    
    let collection = db.GetCollection<Foo>()
    
    collection.Insert(demoFoo) |> ignore
    let indexEnsured = collection.EnsureIndex(fun x -> x.Id)
    printfn "Index ensured: %b" indexEnsured
    
    let allFoos = collection.FindAll() |> Seq.toList
    printfn "Total: %i" allFoos.Length
    
    let result = collection.FindById(BsonValue(id))
    printfn "Last one: %s" (result.Id.ToString())
    0

Do you think there is a way to teach the mapper how to handle DU’s for such a case?

Thomas

[aspnetde]

I think we can consider this done 👍

[Zaid-Ajaj]

I wondered if the readme is wrong or why all the methods are written in lower case there - now I know 😉

I used lower case functions for fsharp queries to distinguish them from the ones used with C# (upper case). You should almost always use the lower case ones.

Doing so results in an exception, as a DU isn’t a proper BsonValue.

My bad, should be fixed now, update nuget from 2.13.0 -> 2.14.0