Added note to say that searching on extra fields with the database backend is not supported

docs/core_components/search/for_python_developers.rst

@@ -36,6 +36,11 @@ Indexing extra fields
     The ``indexed_fields`` configuration format was replaced with ``search_fields``
 
 
+.. note::
+
+    Searching on extra fields with the database backend is not currently supported.
+
+
 Fields need to be explicitly added to the search configuration in order for you to be able to search/filter on them.
 
 You can add new fields to the search index by overriding the ``search_fields`` property and appending a list of extra ``SearchField``/``FilterField`` objects to it.