Use select to True on create_date

If the index is created only in __register__ then it is dropped before being
created again.

issue11197
review389881002
(grafted from b6547efd68b65333187775ad1a01416bee2e3043)

--HG--
branch : 6.0

purchase.py

@@ -243,6 +243,7 @@ class Purchase(
     @classmethod
     def __setup__(cls):
         super(Purchase, cls).__setup__()
+        cls.create_date.select = True
         cls._order = [
             ('purchase_date', 'DESC NULLS FIRST'),
             ('id', 'DESC'),
@@ -363,9 +364,6 @@ class Purchase(
                     values=['processing'],
                     where=sql_table.id.in_(sub_query.select(sub_query.id))))
 
-        # Add index on create_date
-        table.index_action('create_date', action='add')
-
         # Migration from 5.6: rename state cancel to cancelled
         cursor.execute(*sql_table.update(
                 [sql_table.state], ['cancelled'],