Support for Nullable DateTime

LiteDB.FSharp.Tests/Tests.LiteDatabase.fs

@@ -47,6 +47,11 @@ type RecOptGuid = {
     OtherId: Option<Guid>
 }
 
+type RecNullableDateTime = {
+    Id: int
+    Date: Nullable<DateTime>
+}
+
 let pass() = Expect.isTrue true "passed"
 let fail() = Expect.isTrue false "failed"
 
@@ -658,4 +663,32 @@ let liteDatabaseUsage mapper =
                 |> function
                     | 1 -> pass()
                     | n -> fail()
+
+        testCase "Documents with Nullable DateTime != null can be used" <| fun _ ->
+            useDatabase mapper<| fun db ->
+                let docs = db.GetCollection<RecNullableDateTime>()
+                let date = Nullable DateTime.MinValue
+                docs.Insert ({ Id = 1; Date = date }) |> ignore
+                docs.FindAll()
+                |> Seq.tryHead
+                |> function
+                    | None -> fail()
+                    | Some doc ->
+                        match doc.Id, doc.Date with
+                        | 1, date -> pass()
+                        | _ -> fail()
+
+        testCase "Documents with Nullable DateTime = null can be used" <| fun _ ->
+            useDatabase mapper<| fun db ->
+                let docs = db.GetCollection<RecNullableDateTime>()
+                let date = Nullable()
+                docs.Insert ({ Id = 1; Date = date }) |> ignore
+                docs.FindAll()
+                |> Seq.tryHead
+                |> function
+                    | None -> fail()
+                    | Some doc ->
+                        match doc.Id, doc.Date with
+                        | 1, date -> pass()
+                        | _ -> fail()
     ]

LiteDB.FSharp.Tests/Tests.Runner.fs

@@ -1,5 +1,6 @@
 module Runner
 
+open System
 open Expecto
 open Expecto.Logging
 open LiteDB.FSharp
@@ -27,6 +28,10 @@ let defaultValueTests =
         testCase "Default of string is an empty string" <| fun _ ->
             let value = DefaultValue.fromType (typeof<string>) |> unbox<string>
             Expect.equal "" value "An empty string is the default string"
+
+        testCase "Works with Nullable DateTimes" <| fun _ ->
+            let value = DefaultValue.fromType (typeof<Nullable<DateTime>>) |> unbox<Nullable<DateTime>>
+            Expect.equal (Nullable()) value ""
     ]
 
 let liteDbTests mapper name =

LiteDB.FSharp/Json.fs

@@ -44,6 +44,7 @@ type Kind =
     | ObjectId = 13
     | Double = 14
     | Record = 15
+    | NullableDateTime = 16
 
 /// Helper for serializing map/dict with non-primitive, non-string keys such as unions and records.
 /// Performs additional serialization/deserialization of the key object and uses the resulting JSON
@@ -204,6 +205,8 @@ type FSharpJsonConverter() =
                     && t.GetGenericArguments().[0] <> typeof<string>
                 then
                     Kind.MapOrDictWithNonStringKey
+                elif t = typeof<Nullable<DateTime>>
+                then Kind.NullableDateTime
                 else Kind.Other)
 
         match kind with
@@ -297,7 +300,8 @@ type FSharpJsonConverter() =
                     writer.WritePropertyName(fieldType.Name)
                     serializer.Serialize(writer, fieldValue)
                 writer.WriteEndObject()
-
+            | true, Kind.NullableDateTime ->
+                serializer.Serialize(writer, value)
             | true, _ ->
                 serializer.Serialize(writer, value)
 
@@ -457,6 +461,15 @@ type FSharpJsonConverter() =
                 | false, _ -> DefaultValue.fromType fieldType
 
             FSharpValue.MakeRecord(t, recordValues)
+        | true, Kind.NullableDateTime ->
+            match reader.TokenType with
+            | JsonToken.Null ->
+                null
+            | _ ->
+                let jsonObject = JObject.Load(reader)
+                let dateValue = jsonObject.["$date"].Value<string>()
+                let date = DateTime.Parse(dateValue, CultureInfo.InvariantCulture, DateTimeStyles.RoundtripKind)
+                upcast date
 
         | true, _ ->
             serializer.Deserialize(reader, t)