Make EmbeddedModelField.validate() check value type

django_mongodb_backend/fields/embedded_model.py

@@ -1,7 +1,7 @@
 import difflib
 
 from django.core import checks
-from django.core.exceptions import FieldDoesNotExist
+from django.core.exceptions import FieldDoesNotExist, ValidationError
 from django.db import models
 from django.db.models.fields.related import lazy_related_operation
 from django.db.models.lookups import Transform
@@ -134,8 +134,11 @@ def get_transform(self, name):
 
     def validate(self, value, model_instance):
         super().validate(value, model_instance)
-        if self.embedded_model is None:
-            return
+        if not isinstance(value, self.embedded_model):
+            raise ValidationError(
+                f"Expected instance of type {self.embedded_model!r}, not {type(value)!r}."
+            )
+
         for field in self.embedded_model._meta.fields:
             attname = field.attname
             field.validate(getattr(value, attname), model_instance)

tests/model_fields_/test_embedded_model.py

@@ -50,6 +50,16 @@ def test_validate(self):
         with self.assertRaisesMessage(ValidationError, msg):
             obj.full_clean()
 
+    def test_validate_wrong_model_type(self):
+        obj = Holder(data=Library())
+        msg = (
+            "{'data': [\"Expected instance of type "
+            "<class 'model_fields_.models.Data'>, not "
+            "<class 'model_fields_.models.Library'>.\"]}"
+        )
+        with self.assertRaisesMessage(ValidationError, msg):
+            obj.full_clean()
+
 
 class ModelTests(TestCase):
     def test_save_load(self):