docs: def db(self, connection_string=None):
          """Gets the SQLALchemy session for this request"""
  
          connection_string = connection_string or self.settings["db"]
  
          if not hasattr(self, "_db_conns"):
              self._db_conns = {}
          if not connection_string in self._db_conns:
              self._db_conns[connection_string] = oz.sqlalchemy.session(connection_string=connection_string)
  
          return self._db_conns[connection_string]