SqlSession session = shardIdsToShards.get(shardId).establishSqlSession();
IdGenerator idGenerator = shardedSqlSessionFactory.getIdGenerator();
if (idGenerator != null) {
//TODO(fengkuok) 生成主键 DB生成主键是用专有session?
Serializable id = idGenerator.generate(session, parameter);
log.debug(String
.format("Generating id for object %s ,the type of IdGenerator is %s and generated Id is %s.",
parameter.getClass(), idGenerator.getClass(), id));