From 337ec30b6d5c7ce09904438efaa9442b58765dc1 Mon Sep 17 00:00:00 2001
From: ohmayr <omairn@google.com>
Date: Wed, 16 Sep 2026 22:56:59 +0000
Subject: [PATCH] feat(firestore): add PyMongo duck-typing serialization
 support

---
 .../google/cloud/firestore_v1/_helpers.py     | 26 ++++++++++++++++
 .../tests/unit/v1/test__helpers.py            | 30 +++++++++++++++++++
 2 files changed, 56 insertions(+)

diff --git a/packages/google-cloud-firestore/google/cloud/firestore_v1/_helpers.py b/packages/google-cloud-firestore/google/cloud/firestore_v1/_helpers.py
index 51f288f9a84c..258bba65d5f8 100644
--- a/packages/google-cloud-firestore/google/cloud/firestore_v1/_helpers.py
+++ b/packages/google-cloud-firestore/google/cloud/firestore_v1/_helpers.py
@@ -214,6 +214,32 @@ def encode_value(value) -> types.document.Value:
     if isinstance(value, _BSONType):
         return encode_value(value._to_map_value())
 
+    # Duck-type native PyMongo / third-party BSON objects
+    if hasattr(value, "__class__"):
+        cls_name = value.__class__.__name__
+        if cls_name == "ObjectId" and hasattr(value, "binary"):
+            return encode_value({"__oid__": str(value).lower()})
+        if cls_name == "Decimal128" and hasattr(value, "to_decimal"):
+            return encode_value({"__decimal128__": str(value)})
+        if cls_name == "Regex" and hasattr(value, "pattern"):
+            opts = getattr(value, "flags", "") or getattr(value, "options", "")
+            return encode_value(
+                {"__regex__": {"pattern": value.pattern, "options": str(opts)}}
+            )
+        if cls_name == "Timestamp" and hasattr(value, "time") and hasattr(value, "inc"):
+            return encode_value(
+                {
+                    "__request_timestamp__": {
+                        "seconds": value.time,
+                        "increment": value.inc,
+                    }
+                }
+            )
+        if cls_name == "MinKey":
+            return encode_value({"__min__": None})
+        if cls_name == "MaxKey":
+            return encode_value({"__max__": None})
+
     if isinstance(value, GeoPoint):
         return document.Value(geo_point_value=value.to_protobuf())
 
diff --git a/packages/google-cloud-firestore/tests/unit/v1/test__helpers.py b/packages/google-cloud-firestore/tests/unit/v1/test__helpers.py
index b0b81eb98e51..88a493711d50 100644
--- a/packages/google-cloud-firestore/tests/unit/v1/test__helpers.py
+++ b/packages/google-cloud-firestore/tests/unit/v1/test__helpers.py
@@ -46,6 +46,36 @@ def test_geopoint_to_protobuf():
     assert result == geo_pt_pb
 
 
+def test_encode_value_pymongo_duck_typing():
+    from google.cloud.firestore_v1._helpers import encode_value
+
+    class ObjectId:
+        def __init__(self, val):
+            self.val = val
+            self.binary = b"12bytes_raw_"
+
+        def __str__(self):
+            return self.val
+
+    class Decimal128:
+        def __init__(self, val):
+            self.val = val
+
+        def to_decimal(self):
+            return self.val
+
+        def __str__(self):
+            return self.val
+
+    oid_obj = ObjectId("507f191e810c19729de860ea")
+    oid_pb = encode_value(oid_obj)
+    assert oid_pb.map_value.fields["__oid__"].string_value == "507f191e810c19729de860ea"
+
+    dec_obj = Decimal128("123.45")
+    dec_pb = encode_value(dec_obj)
+    assert dec_pb.map_value.fields["__decimal128__"].string_value == "123.45"
+
+
 def test_geopoint___eq__w_same_value():
     lat = 0.015625
     lng = 20.03125