From 38703acc299740ea52a73cca3e222bc050754223 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastien=20G=C3=A9rard?= <bastien.gerard@cluepoints.com>
Date: Thu, 23 Jan 2020 23:33:23 +0100
Subject: [PATCH 1/2] fix complex datetime field invalid string set

---
 mongoengine/fields.py                       |  5 ++++-
 tests/fields/test_complex_datetime_field.py | 17 +++++++++++++++++
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/mongoengine/fields.py b/mongoengine/fields.py
index 7ec8c0f3..3eff0325 100644
--- a/mongoengine/fields.py
+++ b/mongoengine/fields.py
@@ -684,7 +684,10 @@ class ComplexDateTimeField(StringField):
         super(ComplexDateTimeField, self).__set__(instance, value)
         value = instance._data[self.name]
         if value is not None:
-            instance._data[self.name] = self._convert_from_datetime(value)
+            if isinstance(value, datetime.datetime):
+                instance._data[self.name] = self._convert_from_datetime(value)
+            else:
+                instance._data[self.name] = value
 
     def validate(self, value):
         value = self.to_python(value)
diff --git a/tests/fields/test_complex_datetime_field.py b/tests/fields/test_complex_datetime_field.py
index f0a6b96e..699032cc 100644
--- a/tests/fields/test_complex_datetime_field.py
+++ b/tests/fields/test_complex_datetime_field.py
@@ -4,6 +4,8 @@ import itertools
 import math
 import re
 
+import pytest
+
 from mongoengine import *
 
 from tests.utils import MongoDBTestCase
@@ -191,3 +193,18 @@ class ComplexDateTimeFieldTest(MongoDBTestCase):
 
         fetched_log = Log.objects.with_id(log.id)
         assert fetched_log.timestamp >= NOW
+
+    def test_setting_bad_value_does_not_raise_unless_validate_is_called(self):
+        # test regression of #2253
+
+        class Log(Document):
+            timestamp = ComplexDateTimeField()
+
+        Log.drop_collection()
+
+        log = Log(timestamp="garbage")
+        with pytest.raises(ValidationError):
+            log.validate()
+
+        with pytest.raises(ValidationError):
+            log.save()

From 2d6a4c4b9043d5cf4fe029870fceb9ecd47ce9af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bastien=20G=C3=A9rard?= <bastien.gerard@cluepoints.com>
Date: Thu, 23 Jan 2020 23:36:03 +0100
Subject: [PATCH 2/2] update changelog

---
 docs/changelog.rst | 1 +
 1 file changed, 1 insertion(+)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index d924a2c1..11e6c063 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -7,6 +7,7 @@ Development
 ===========
 - (Fill this out as you fix issues and develop your features).
 - Add Mongo 4.0 to Travis
+- Fix error when setting a string as a ComplexDateTimeField #2253
 
 Changes in 0.19.1
 =================