From 8d98ab2535cc2b6c837e1e2e7087941ca3763423 Mon Sep 17 00:00:00 2001
From: njlr <njlr@users.noreply.github.com>
Date: Sat, 6 Jun 2026 13:00:03 +0100
Subject: [PATCH 1/2] Adds Codec.optional

---
 tests/ObjectCodec.fs       | 25 +++++++++++++++++++++++++
 thoth-json-codec/Object.fs | 14 ++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/tests/ObjectCodec.fs b/tests/ObjectCodec.fs
index a42d9c9..d018228 100644
--- a/tests/ObjectCodec.fs
+++ b/tests/ObjectCodec.fs
@@ -8,6 +8,7 @@ open Fable.Mocha
 open Expecto
 #endif
 
+open Thoth.Json.Core
 open Thoth.Json.Codec
 open Thoth.Json.Codec.Tests
 
@@ -31,6 +32,8 @@ type Large =
     Baz : Guid
   }
 
+type Baz = { Baz : string option }
+
 module Codec =
 
   let fooBar : Codec<FooBar> =
@@ -73,6 +76,13 @@ module Codec =
         }
     }
 
+  let baz : Codec<Baz> =
+    objectCodec {
+      let! baz = Codec.optional "baz" (fun x -> x.Baz) Codec.string
+
+      return { Baz = baz }
+    }
+
 let tests =
   testList
     "ObjectCodec"
@@ -118,4 +128,19 @@ let tests =
 
         Expect.equal actual expected "The decoded value must match the original"
       }
+
+      test "objectCodec optional field works" {
+        let withValue = { Baz = Some "abc" }
+
+        let withoutValue = { Baz = None }
+
+        let actualWithValue =
+          roundTrip Codec.baz withValue
+
+        let actualWithoutValue =
+          roundTrip Codec.baz withoutValue
+
+        Expect.equal actualWithValue withValue "The decoded Some value must match the original"
+        Expect.equal actualWithoutValue withoutValue "The decoded None value must match the original"
+      }
     ]
diff --git a/thoth-json-codec/Object.fs b/thoth-json-codec/Object.fs
index 853fee4..a9f2095 100644
--- a/thoth-json-codec/Object.fs
+++ b/thoth-json-codec/Object.fs
@@ -49,3 +49,17 @@ module ObjectCodecComputationExpression =
         Decoder = Decode.field fieldName fieldCodec.Decoder
         Picker = picker
       }
+
+    let optional
+      (fieldName : string)
+      (picker : 'u -> 't option)
+      (fieldCodec : Codec<'t>)
+      : ObjectCodecFieldSet<'t option, 'u> =
+      {
+        Values =
+          function
+          | Some i -> [ fieldName, fieldCodec.Encoder i ]
+          | None -> []
+        Decoder = Decode.optional fieldName fieldCodec.Decoder
+        Picker = picker
+      }

From 21e566d9b2bb1c79aad132e374b30194d86ef00c Mon Sep 17 00:00:00 2001
From: njlr <njlr@users.noreply.github.com>
Date: Sat, 6 Jun 2026 13:03:41 +0100
Subject: [PATCH 2/2] Unused import

---
 tests/ObjectCodec.fs | 1 -
 1 file changed, 1 deletion(-)

diff --git a/tests/ObjectCodec.fs b/tests/ObjectCodec.fs
index d018228..fdb1eb1 100644
--- a/tests/ObjectCodec.fs
+++ b/tests/ObjectCodec.fs
@@ -8,7 +8,6 @@ open Fable.Mocha
 open Expecto
 #endif
 
-open Thoth.Json.Core
 open Thoth.Json.Codec
 open Thoth.Json.Codec.Tests