Updates flow objects in the database.

def UpdateFlows(self,
                  client_id_flow_id_pairs,
                  pending_termination=db.Database.unchanged,
                  cursor=None):
    """Updates flow objects in the database."""

    if pending_termination == db.Database.unchanged:
      return

    serialized_termination = pending_termination.SerializeToString()
    query = "UPDATE flows SET pending_termination=%s WHERE "
    args = [serialized_termination]
    for index, (client_id, flow_id) in enumerate(client_id_flow_id_pairs):
      query += ("" if index == 0 else " OR ") + " client_id=%s AND flow_id=%s"
      args.extend(
          [db_utils.ClientIDToInt(client_id),
           db_utils.FlowIDToInt(flow_id)])
    cursor.execute(query, args)