[IMP] pg.named_cursor: lessons learned from pg.query_ids

- it is not exactly right to call into the `Cursor`'s `__enter__` and
  `__exit__` methods
- `Cursor` should be explicitly closed before it is garbage collected

Author: cawo-odoo

src/util/pg.py

@@ -1770,6 +1770,7 @@ def get_m2m_tables(cr, table):
 
 class named_cursor(object):
     def __init__(self, cr, itersize=None):
+        self._ncr = None
         self._ncr = cr._cnx.cursor("upg_nc_" + uuid.uuid4().hex, withhold=True)
         if itersize:
             self._ncr.itersize = itersize
@@ -1790,19 +1791,26 @@ def dictfetchone(self):
     def iterdict(self):
         return map(self.__dictrow, self._ncr)
 
+    def _close(self):
+        if self._ncr and not self._ncr.closed:
+            self._ncr.close()
+
     def __iter__(self):
         return self._ncr.__iter__()
 
     def __enter__(self):
-        self._ncr.__enter__()
         return self
 
     def __exit__(self, exc_type, exc_value, traceback):
-        return self._ncr.__exit__(exc_type, exc_value, traceback)
+        self._close()
+        return False
 
     def __getattr__(self, name):
         return getattr(self._ncr, name)
 
+    def __del__(self):
+        self._close()
+
 
 def create_id_sequence(cr, table, set_as_default=True):
     if not table_exists(cr, table):