hibernate中session的三种状态：

瞬时状态：没有被session所管理且数据库中没有。

持久化状态：被session所管理但是数据库中没有。

离线状态：数据库中存在但是未被session所管理。

下面是几个小例子：

瞬时状态-->持久化状态01

输出：

Hibernate: insert into t_user (username, password, nikename, born) values (?, ?, ?, ?)

瞬时状态-->持久化状态02

输出：

Hibernate: insert into t_user (username, password, nikename, born) values (?, ?, ?, ?)

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

update的执行时机

输出：

Hibernate: insert into t_user (username, password, nikename, born) values (?, ?, ?, ?)

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

save或update的执行与否

输出：

Hibernate: insert into t_user (username, password, nikename, born) values (?, ?, ?, ?)

load也会使对象变为持久化状态

输出：

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.nikename as nikename0_0_, user0_.born as born0_0_ from t_user user0_ where user0_.id=?

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

两次事务共享session

输出：

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.nikename as nikename0_0_, user0_.born as born0_0_ from t_user user0_ where user0_.id=?

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

save操作

输出：

Hibernate: insert into t_user (username, password, nikename, born) values (?, ?, ?, ?)

在提交update的时候 怎么发出的sql语句？？？

个人理解：如果该id对应的对象在数据库中不存在，则会抛出异常，如果数据库中存在，就会update，至于update的和session里的数据比较是不手动update才会触发的，如果直接执行update就不会再去session里比较了。

输出：

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

输出：

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

输出：

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.nikename as nikename0_0_, user0_.born as born0_0_ from t_user user0_ where user0_.id=?

输出：

Hibernate: select user0_.id as id0_0_, user0_.username as username0_0_, user0_.password as password0_0_, user0_.nikename as nikename0_0_, user0_.born as born0_0_ from t_user user0_ where user0_.id=?

Hibernate: update t_user set username=?, password=?, nikename=?, born=? where id=?

个人理解：对比以上两个输出可以发现，手动update的时候不会和session中缓存进行比较，直接update，当不是手动update的时候，回和session缓存进行比较