UnionConverter: Handle Nested Unions

CHANGELOG.md

@@ -13,6 +13,7 @@ The `Unreleased` section name is replaced by the expected version of next releas
 ### Removed
 ### Fixed
 
+- `UnionConverter`: Handle nested unions [#52](https://github.com/jet/FsCodec/pull/52)
 - `UnionConverter`: Support overriding discriminator without needing to nominate a `catchAllCase` [#51](https://github.com/jet/FsCodec/pull/51)
 
 <a name="2.1.0"></a>

src/FsCodec.NewtonsoftJson/UnionConverter.fs

@@ -31,7 +31,7 @@ module private Union =
 
  let getUnion = memoize createUnion
 
- /// Paralells F# behavior wrt how it generates a DU's underlying .NET Type
+ /// Parallels F# behavior wrt how it generates a DU's underlying .NET Type
  let inline isInlinedIntoUnionItem (t : Type) =
  t = typeof<string>
  || t.IsValueType
@@ -41,6 +41,7 @@ module private Union =
  || t.GetGenericTypeDefinition().IsValueType)) // Nullable<T>
 
  let typeHasJsonConverterAttribute = memoize (fun (t : Type) -> t.IsDefined(typeof<JsonConverterAttribute>))
+ let typeIsUnionWithConverterAttribute = memoize (fun (t : Type) -> isUnion t && typeHasJsonConverterAttribute t)
 
  let propTypeRequiresConstruction (propertyType : Type) =
  not (isInlinedIntoUnionItem propertyType)
@@ -91,7 +92,7 @@ type UnionConverter private (discriminator : string, ?catchAllCase) =
  writer.WriteValue(case.Name)
 
  match fieldInfos with
- | [| fi |] ->
+ | [| fi |] when not (Union.typeIsUnionWithConverterAttribute fi.PropertyType) ->
  match fieldValues.[0] with
  | null when serializer.NullValueHandling = NullValueHandling.Ignore -> ()
  | fv ->

tests/FsCodec.NewtonsoftJson.Tests/UnionConverterTests.fs

@@ -371,3 +371,118 @@ module ``Unmatched case handling`` =
  && string jo.["case"]="CaseUnknown" @>
  let expected = "{\r\n \"case\": \"CaseUnknown\",\r\n \"a\": \"s\",\r\n \"b\": 1,\r\n \"c\": true\r\n}".Replace("\r\n",Environment.NewLine)
  test <@ expected = string jo @>
+
+module Nested =
+
+ [<JsonConverter(typeof<UnionConverter>)>]
+ type U =
+ | B of NU
+ | C of UUA
+ | D of UU
+ | E of E
+ | EA of E[]
+ | R of {| a : int; b : NU |}
+ | S
+ and [<JsonConverter(typeof<UnionConverter>)>]
+ NU =
+ | A of string
+ | B of int
+ | R of {| a : int; b : NU |}
+ | S
+ and [<JsonConverter(typeof<UnionConverter>)>]
+ UU =
+ | A of string
+ | B of int
+ | E of E
+ | EO of E option
+ | R of {| a: int; b: string |}
+ | S
+ and [<JsonConverter(typeof<UnionConverter>, "case2")>]
+ UUA =
+ | A of string
+ | B of int
+ | E of E
+ | EO of E option
+ | R of {| a: int; b: string |}
+ | S
+ and [<JsonConverter(typeof<TypeSafeEnumConverter>)>]
+ E =
+ | V1
+ | V2
+
+ let [<FsCheck.Xunit.Property>] ``can nest`` (value : U) =
+ let ser = Serdes.Serialize value
+ test <@ value = Serdes.Deserialize ser @>
+
+ let [<Fact>] ``nesting Unions represents child as item`` () =
+ let v : U = U.C(UUA.B 42)
+ let ser = Serdes.Serialize v
+ """{"case":"C","Item":{"case2":"B","Item":42}}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let [<Fact>] ``TypeSafeEnum converts direct`` () =
+ let v : U = U.C (UUA.E E.V1)
+ let ser = Serdes.Serialize v
+ """{"case":"C","Item":{"case2":"E","Item":"V1"}}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let v : U = U.E E.V2
+ let ser = Serdes.Serialize v
+ """{"case":"E","Item":"V2"}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let v : U = U.EA [|E.V2; E.V2|]
+ let ser = Serdes.Serialize v
+ """{"case":"EA","Item":["V2","V2"]}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let v : U = U.C (UUA.EO (Some E.V1))
+ let ser = Serdes.Serialize v
+ """{"case":"C","Item":{"case2":"EO","Item":"V1"}}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let v : U = U.C (UUA.EO None)
+ let ser = Serdes.Serialize v
+ """{"case":"C","Item":{"case2":"EO","Item":null}}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let v : U = U.C UUA.S
+ let ser = Serdes.Serialize v
+ """{"case":"C","Item":{"case2":"S"}}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+/// And for everything else, JsonIsomorphism allows plenty ways of customizing the encoding and/or decoding
+module IsomorphismUnionEncoder =
+
+ type [<JsonConverter(typeof<TopConverter>)>]
+ Top =
+ | S
+ | N of Nested
+ and Nested =
+ | A
+ | B of int
+ and TopConverter() =
+ inherit JsonIsomorphism<Top, Flat<int>>()
+ override __.Pickle value =
+ match value with
+ | S -> { disc = TS; v = None }
+ | N A -> { disc = TA; v = None }
+ | N (B v) -> { disc = TB; v = Some v }
+ override __.UnPickle flat =
+ match flat with
+ | { disc = TS } -> S
+ | { disc = TA } -> N A
+ | { disc = TB; v = v} -> N (B (Option.get v))
+ and Flat<'T> = { disc : JiType; v : 'T option }
+ and [<JsonConverter(typeof<TypeSafeEnumConverter>)>]
+ JiType = TS | TA | TB
+
+ let [<Fact>] ``Can control the encoding to the nth degree`` () =
+ let v : Top = N (B 42)
+ let ser = Serdes.Serialize v
+ """{"disc":"TB","v":42}""" =! ser
+ test <@ v = Serdes.Deserialize ser @>
+
+ let [<FsCheck.Xunit.Property>] ``can roundtrip`` (value : Top) =
+ let ser = Serdes.Serialize value
+ test <@ value = Serdes.Deserialize ser @>