docs: def connection(self):
          """Connect to and return mongodb database object."""
          if self._connection is None:
  
              self._connection = self.client[self.database_name]
  
              if self.disable_id_injector:
                  incoming = self._connection._Database__incoming_manipulators
                  for manipulator in incoming:
                      if isinstance(manipulator,
                                    pymongo.son_manipulator.ObjectIdInjector):
                          incoming.remove(manipulator)
                          LOG.debug("Disabling %s on mongodb connection to "
                                    "'%s'.",
                                    manipulator.__class__.__name__,
                                    self.database_name)
                          break
  
              for manipulator in self.manipulators:
                  self._connection.add_son_manipulator(manipulator)
              LOG.info("Connected to mongodb on %s (database=%s)",
                       self.safe_connection_string, self.database_name)
  
          return self._connection