Test case and proposed solution for #2484

AUTHORS

@@ -259,3 +259,4 @@ that much better:
  * Agustin Barto (https://github.com/abarto)
  * Stankiewicz Mateusz (https://github.com/mas15)
  * Felix Schultheiß (https://github.com/felix-smashdocs)
+ * Jan Stein (https://github.com/janste63)

docs/changelog.rst

@@ -7,6 +7,7 @@ Development
 ===========
 - (Fill this out as you fix issues and develop your features).
 - Bugfix: manually setting SequenceField in DynamicDocument doesn't increment the counter #2471
+- Bug fix: ignore LazyReferenceFields when clearing _changed_fields #2484
 
 Changes in 0.22.1
 =================

mongoengine/base/document.py

@@ -615,7 +615,9 @@ class BaseDocument:
     def _get_changed_fields(self):
         """Return a list of all fields that have explicitly been changed."""
         EmbeddedDocument = _import_class("EmbeddedDocument")
+        LazyReferenceField = _import_class("LazyReferenceField")
         ReferenceField = _import_class("ReferenceField")
+        GenericLazyReferenceField = _import_class("GenericLazyReferenceField")
         GenericReferenceField = _import_class("GenericReferenceField")
         SortedListField = _import_class("SortedListField")
 
@@ -641,7 +643,13 @@ class BaseDocument:
                 changed_fields += [f"{key}{k}" for k in changed if k]
             elif isinstance(data, (list, tuple, dict)):
                 if hasattr(field, "field") and isinstance(
-                    field.field, (ReferenceField, GenericReferenceField)
+                    field.field,
+                    (
+                        LazyReferenceField,
+                        ReferenceField,
+                        GenericLazyReferenceField,
+                        GenericReferenceField,
+                    ),
                 ):
                     continue
                 elif isinstance(field, SortedListField) and field._ordering:

tests/fields/test_lazy_reference_field.py

@@ -375,6 +375,26 @@ class TestLazyReferenceField(MongoDBTestCase):
             assert isinstance(ref.author, LazyReference)
             assert isinstance(ref.author.id, ObjectId)
 
+    def test_lazy_reference_in_list_with_changed_element(self):
+        class Animal(Document):
+            name = StringField()
+            tag = StringField()
+
+        class Ocurrence(Document):
+            in_list = ListField(LazyReferenceField(Animal))
+
+        Animal.drop_collection()
+        Ocurrence.drop_collection()
+
+        animal1 = Animal(name="doggo").save()
+
+        animal1.tag = "blue"
+
+        occ = Ocurrence(in_list=[animal1]).save()
+        animal1.save()
+        assert isinstance(occ.in_list[0], LazyReference)
+        assert occ.in_list[0].pk == animal1.pk
+
 
 class TestGenericLazyReferenceField(MongoDBTestCase):
     def test_generic_lazy_reference_simple(self):