Add new UnionMode

FSharp.Json.Tests/Union.fs

@@ -95,7 +95,32 @@ module Union =
         let actual = Json.serializeU value
         let expected = """{"casekey":"StringCase","casevalue":"The string"}"""
         Assert.AreEqual(expected, actual)
-
+
+    [<JsonUnion(Mode = UnionMode.AsValue)>]
+    type AsValueUnion =
+    | StringCase of string
+    | IntCase of int
+
+    type RecordWithAsValueUnion = {
+        StringValue : AsValueUnion
+        IntValue : AsValueUnion
+    }
+
+    [<Test>]
+    let ``Union AsValue serialization`` () =
+        let record = { StringValue = StringCase "String"; IntValue = IntCase 1 }
+        let actual = Json.serializeU record
+        let expected = """{"StringValue":"String","IntValue":1}"""
+        Assert.AreEqual(expected, actual)
+
+    [<Test>]
+    let ``Union AsValue deserialization`` () =
+        let json = """{"StringValue":"String"}"""
+        let ex = Assert.Throws<JsonDeserializationError>(fun () -> Json.deserialize<RecordWithAsValueUnion> json |> ignore)
+        Assert.IsNotNull(ex)
+        let expectedPath = "StringValue"
+        Assert.AreEqual(expectedPath, ex.Path.toString())
+
     [<Test>]
     let ``Union key-value deserialization`` () =
         let expected = TheAnnotatedUnion.StringCase "The string"

FSharp.Json/Core.fs

@@ -1,5 +1,8 @@
 namespace FSharp.Json
 
+open FSharp.Json
+open FSharp.Json.Internalized.FSharp.Data
+
 module internal Core =
     open System
     open System.Globalization
@@ -249,6 +252,7 @@ module internal Core =
                         let jkey = (jsonUnion.CaseKeyField, JsonValue.String theCase)
                         let jvalue = (jsonUnion.CaseValueField, jvalue)
                         JsonValue.Record [| jkey; jvalue |]
+                    | UnionMode.AsValue -> jvalue
                     | UnionMode.CaseKeyDiscriminatorField ->
                         match jvalue with
                         | JsonValue.Record jrecord ->
@@ -515,6 +519,7 @@ module internal Core =
                 FSharpValue.MakeUnion (caseInfo, values)
             | _ ->
                 match jvalue with
+                | _ when jsonUnion.Mode = UnionMode.AsValue -> failDeserialization path "Failed to parse union from JSON: Union with AsValue Mode can't be parsed"
                 | JsonValue.String caseName ->
                     FSharpValue.MakeUnion (caseName |> getUnionCaseInfo path t, null)
                 | JsonValue.Record fields ->

FSharp.Json/InterfaceTypes.fs

@@ -50,6 +50,8 @@ type UnionMode =
     | CaseKeyAsFieldValue = 1
     /// Serialize union case key as discriminator field value.
     | CaseKeyDiscriminatorField = 2
+    /// Serialize union case as value.
+    | AsValue = 3
 
 /// Attribute customizing serialization of union types
 type JsonUnion () =