diff --git a/AUTHORS b/AUTHORS
index 88d4bbe1..4eac5eb2 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -243,4 +243,5 @@ that much better:
  * Victor Varvaryuk
  * Stanislav Kaledin (https://github.com/sallyruthstruik)
  * Dmitry Yantsen (https://github.com/mrTable)
- * Erdenezul Batmunkh (https://github.com/erdenezul)
+ * Renjianxin (https://github.com/Davidrjx)
+ * Erdenezul Batmunkh (https://github.com/erdenezul)
\ No newline at end of file
diff --git a/mongoengine/connection.py b/mongoengine/connection.py
index 7eae810f..34ff4dc3 100644
--- a/mongoengine/connection.py
+++ b/mongoengine/connection.py
@@ -146,13 +146,14 @@ def get_connection(alias=DEFAULT_CONNECTION_NAME, reconnect=False):
         raise MongoEngineConnectionError(msg)
 
     def _clean_settings(settings_dict):
-        irrelevant_fields = set([
-            'name', 'username', 'password', 'authentication_source',
-            'authentication_mechanism'
-        ])
+        # set literal more efficient than calling set function
+        irrelevant_fields_set = {
+            'name', 'username', 'password',
+            'authentication_source', 'authentication_mechanism'
+        }
         return {
             k: v for k, v in settings_dict.items()
-            if k not in irrelevant_fields
+            if k not in irrelevant_fields_set
         }
 
     # Retrieve a copy of the connection settings associated with the requested
diff --git a/mongoengine/queryset/base.py b/mongoengine/queryset/base.py
index f7c32d20..6f9c372c 100644
--- a/mongoengine/queryset/base.py
+++ b/mongoengine/queryset/base.py
@@ -1722,25 +1722,33 @@ class BaseQuerySet(object):
         return frequencies
 
     def _fields_to_dbfields(self, fields):
-        """Translate fields paths to its db equivalents"""
-        ret = []
+        """Translate fields' paths to their db equivalents."""
         subclasses = []
-        document = self._document
-        if document._meta['allow_inheritance']:
+        if self._document._meta['allow_inheritance']:
             subclasses = [get_document(x)
-                          for x in document._subclasses][1:]
+                          for x in self._document._subclasses][1:]
+
+        db_field_paths = []
         for field in fields:
+            field_parts = field.split('.')
             try:
-                field = '.'.join(f.db_field for f in
-                                 document._lookup_field(field.split('.')))
-                ret.append(field)
+                field = '.'.join(
+                    f if isinstance(f, six.string_types) else f.db_field
+                    for f in self._document._lookup_field(field_parts)
+                )
+                db_field_paths.append(field)
             except LookUpError as err:
                 found = False
+
+                # If a field path wasn't found on the main document, go
+                # through its subclasses and see if it exists on any of them.
                 for subdoc in subclasses:
                     try:
-                        subfield = '.'.join(f.db_field for f in
-                                            subdoc._lookup_field(field.split('.')))
-                        ret.append(subfield)
+                        subfield = '.'.join(
+                            f if isinstance(f, six.string_types) else f.db_field
+                            for f in subdoc._lookup_field(field_parts)
+                        )
+                        db_field_paths.append(subfield)
                         found = True
                         break
                     except LookUpError:
@@ -1748,7 +1756,8 @@ class BaseQuerySet(object):
 
                 if not found:
                     raise err
-        return ret
+
+        return db_field_paths
 
     def _get_order_by(self, keys):
         """Given a list of MongoEngine-style sort keys, return a list
diff --git a/tests/queryset/field_list.py b/tests/queryset/field_list.py
index d1277e06..c07cec3e 100644
--- a/tests/queryset/field_list.py
+++ b/tests/queryset/field_list.py
@@ -197,14 +197,18 @@ class OnlyExcludeAllTest(unittest.TestCase):
             title = StringField()
             text = StringField()
 
+        class VariousData(EmbeddedDocument):
+            some = BooleanField()
+
         class BlogPost(Document):
             content = StringField()
             author = EmbeddedDocumentField(User)
             comments = ListField(EmbeddedDocumentField(Comment))
+            various = MapField(field=EmbeddedDocumentField(VariousData))
 
         BlogPost.drop_collection()
 
-        post = BlogPost(content='Had a good coffee today...')
+        post = BlogPost(content='Had a good coffee today...', various={'test_dynamic':{'some': True}})
         post.author = User(name='Test User')
         post.comments = [Comment(title='I aggree', text='Great post!'), Comment(title='Coffee', text='I hate coffee')]
         post.save()
@@ -215,6 +219,9 @@ class OnlyExcludeAllTest(unittest.TestCase):
         self.assertEqual(obj.author.name, 'Test User')
         self.assertEqual(obj.comments, [])
 
+        obj = BlogPost.objects.only('various.test_dynamic.some').get()
+        self.assertEqual(obj.various["test_dynamic"].some, True)
+
         obj = BlogPost.objects.only('content', 'comments.title',).get()
         self.assertEqual(obj.content, 'Had a good coffee today...')
         self.assertEqual(obj.author, None)