Fix some issues related with db_field in constructor

docs/changelog.rst

@@ -12,6 +12,7 @@ Development
     This should have a negative impact on performance of count see Issue #2219
 - Fix a bug that made the queryset drop the read_preference after clone().
 - Remove Py3.5 from CI as it reached EOL and add Python 3.9
+- Fix some issues related with db_field conflict in constructor #2414
 - Fix the behavior of Doc.objects.limit(0) which should return all documents (similar to mongodb) #2311
 - Bug fix in ListField when updating the first item, it was saving the whole list, instead of
     just replacing the first item (as it's usually done) #2392

mongoengine/base/document.py

@@ -101,12 +101,13 @@ def __init__(self, *args, **values):
 
         self._dynamic_fields = SON()
 
-        # Assign default values to the instance.
-        for key, field in self._fields.items():
-            if self._db_field_map.get(key, key) in values:
+        # Assign default values for fields
+        # not set in the constructor
+        for field_name in self._fields:
+            if field_name in values:
                 continue
-            value = getattr(self, key, None)
-            setattr(self, key, value)
+            value = getattr(self, field_name, None)
+            setattr(self, field_name, value)
 
         if "_cls" not in values:
             self._cls = self._class_name
@@ -115,7 +116,6 @@ def __init__(self, *args, **values):
         dynamic_data = {}
         FileField = _import_class("FileField")
         for key, value in values.items():
-            key = self._reverse_db_field_map.get(key, key)
             field = self._fields.get(key)
             if field or key in ("id", "pk", "_cls"):
                 if __auto_convert and value is not None:
@@ -750,7 +750,8 @@ def _get_collection_name(cls):
 
     @classmethod
     def _from_son(cls, son, _auto_dereference=True, created=False):
-        """Create an instance of a Document (subclass) from a PyMongo SON."""
+        """Create an instance of a Document (subclass) from a PyMongo SON (dict)
+        """
         if son and not isinstance(son, dict):
             raise ValueError(
                 "The source SON object needs to be of type 'dict' but a '%s' was found"
@@ -763,6 +764,8 @@ def _from_son(cls, son, _auto_dereference=True, created=False):
 
         # Convert SON to a data dict, making sure each key is a string and
         # corresponds to the right db field.
+        # This is needed as _from_son is currently called both from BaseDocument.__init__
+        # and from EmbeddedDocumentField.to_python
         data = {}
         for key, value in son.items():
             key = str(key)

tests/document/test_instance.py

@@ -3822,5 +3822,95 @@ class Book(Document):
         assert book._object_key == {"pk": book.pk, "author__name": "Author"}
 
 
+class DBFieldMappingTest(MongoDBTestCase):
+    def setUp(self):
+        class Fields(object):
+            w1 = BooleanField(db_field="w2")
+
+            x1 = BooleanField(db_field="x2")
+            x2 = BooleanField(db_field="x3")
+
+            y1 = BooleanField(db_field="y0")
+            y2 = BooleanField(db_field="y1")
+
+            z1 = BooleanField(db_field="z2")
+            z2 = BooleanField(db_field="z1")
+
+        class Doc(Fields, Document):
+            pass
+
+        class DynDoc(Fields, DynamicDocument):
+            pass
+
+        self.Doc = Doc
+        self.DynDoc = DynDoc
+
+    def tearDown(self):
+        for collection in list_collection_names(self.db):
+            self.db.drop_collection(collection)
+
+    def test_setting_fields_in_constructor_of_strict_doc_uses_model_names(self):
+        doc = self.Doc(z1=True, z2=False)
+        assert doc.z1 is True
+        assert doc.z2 is False
+
+    def test_setting_fields_in_constructor_of_dyn_doc_uses_model_names(self):
+        doc = self.DynDoc(z1=True, z2=False)
+        assert doc.z1 is True
+        assert doc.z2 is False
+
+    def test_setting_unknown_field_in_constructor_of_dyn_doc_does_not_overwrite_model_fields(
+        self,
+    ):
+        doc = self.DynDoc(w2=True)
+        assert doc.w1 is None
+        assert doc.w2 is True
+
+    def test_unknown_fields_of_strict_doc_do_not_overwrite_dbfields_1(self):
+        doc = self.Doc()
+        doc.w2 = True
+        doc.x3 = True
+        doc.y0 = True
+        doc.save()
+        reloaded = self.Doc.objects.get(id=doc.id)
+        assert reloaded.w1 is None
+        assert reloaded.x1 is None
+        assert reloaded.x2 is None
+        assert reloaded.y1 is None
+        assert reloaded.y2 is None
+
+    def test_dbfields_are_loaded_to_the_right_modelfield_for_strict_doc_2(self):
+        doc = self.Doc()
+        doc.x2 = True
+        doc.y2 = True
+        doc.z2 = True
+        doc.save()
+        reloaded = self.Doc.objects.get(id=doc.id)
+        assert (
+            reloaded.x1,
+            reloaded.x2,
+            reloaded.y1,
+            reloaded.y2,
+            reloaded.z1,
+            reloaded.z2,
+        ) == (doc.x1, doc.x2, doc.y1, doc.y2, doc.z1, doc.z2)
+
+    def test_dbfields_are_loaded_to_the_right_modelfield_for_dyn_doc_2(self):
+        doc = self.DynDoc()
+        doc.x2 = True
+        doc.y2 = True
+        doc.z2 = True
+        doc.save()
+        reloaded = self.DynDoc.objects.get(id=doc.id)
+        assert (
+            reloaded.x1,
+            reloaded.x2,
+            reloaded.y1,
+            reloaded.y2,
+            reloaded.z1,
+            reloaded.z2,
+        ) == (doc.x1, doc.x2, doc.y1, doc.y2, doc.z1, doc.z2)
+
+
 if __name__ == "__main__":
     unittest.main()

tests/fields/test_fields.py

@@ -2272,6 +2272,13 @@ class Doc(Document):
         with pytest.raises(FieldDoesNotExist):
             Doc(bar="test")
 
+    def test_undefined_field_works_no_confusion_with_db_field(self):
+        class Doc(Document):
+            foo = StringField(db_field="bar")
+
+        with pytest.raises(FieldDoesNotExist):
+            Doc(bar="test")
+
 
 class TestEmbeddedDocumentListField(MongoDBTestCase):
     def setUp(self):