update the Index with Document mappings before calling save()

Author: honzakral

elasticsearch_dsl/document.py

@@ -131,6 +131,7 @@ def init(cls, index=None, using=None):
         i = cls._index
         if index:
             i = i.clone(name=index)
+        i.document(cls)
         i.save(using=using)
 
     def _get_index(self, index=None, required=True):