09hibernate_session_flush

session flush测试：

session flush方法主要做了两件事：

* 清理缓存

* 执行sql

session在什么情况下执行flush

* 默认在事务提交时

* 显示的调用flush

* 在执行查询前，如：iterate

hibernate按照save(insert),update、delete顺序提交相关操作

uuid:create table t_user1 (user_id varchar(32) not null, name varchar(20) not null unique, password varchar(10) not null, create_time datetime, expire_time datetime, primary key (user_id))

native:create table t_user2 (user_id integer not null auto_increment, name varchar(20) not null unique, password varchar(10) not null, createtime datetime, expiretime datetime, primary key (user_id))

assigned:create table t_user3 (user_id varchar(32) not null, name varchar(255), password varchar(255), create_time datetime, expire_time datetime, primary key (user_id))

/** * 测试uuid主键生成策略1：完成save后不会发出insert语句，直到commit时flush时才发insert语句 */ publicvoid testSave1() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User1 user = new User1(); user.setName("李四3"); user.setPassword("123"); user.setCreateTime(new Date()); user.setExpireTime(new Date()); //因为user的主键生成侧路采用的是uuid，所以调用完成save后，只是将user纳入到了session的管理 //不会发出insert语句，但是id已经生成，session中existsInDatebase状态为false session.save(user);//save后,不发Hibernate: insert into //调用flush，hibernate会清理缓存，执行sql //如果数据库的隔离级别设置为：未提交读read uncommitted，那么我们可以看到flush过的数据 //并且session中existsInDatebase状态为true session.flush();//发Hibernate: insert into //提交事务 //commit后数据是无法回滚的 tx.commit();//默认情况下commit操作会先执行flush清理缓存，所以不用显示的调用flush }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

session.flush();//flush后：发Hibernate: insert into

Hibernate: insert into t_user1 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

没有提交事务前：我们来看一下数据库中有没有记录：

mysql> select @@tx_isolation;

+-----------------+

| @@tx_isolation |

+-----------------+

| REPEATABLE-READ |

+-----------------+

1 row in set (0.03 sec)

mysql> select * from t_user1;

Empty set (0.06 sec)

mysql> set transaction isolation level read uncommitted;

Query OK, 0 rows affected (0.00 sec)

mysql> select @@tx_isolation;

+------------------+

| @@tx_isolation |

+------------------+

| READ-UNCOMMITTED |

+------------------+

1 row in set (0.00 sec)

mysql> select * from t_user1;

+----------------------------------+-------+----------+---------------------+---------------------+

| user_id | name | password | create_time | expire_time |

+----------------------------------+-------+----------+---------------------+---------------------+

| 402881e738eb64e20138eb65f3990001 | 李四3 | 123 | 2012-08-03 15:31:55 | 2012-08-03 15:32:02 |

+----------------------------------+-------+----------+---------------------+---------------------+

1 row in set (0.00 sec)

/** * 测试native主键生成策略:完成save后马上发出insert语句 */ publicvoid testSave2() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User2 user = new User2(); user.setName("猪八戒"); user.setPassword("123"); user.setCreateTime(new Date()); user.setExpireTime(new Date()); //因为user的主键生成策略为native,所以调用session.save后，将执行insert语句，返回有数据库生成的id //纳入了session的管理，修改了session中existsInDatebase状态为true //如果数据库的隔离级别设置为：未提交读read uncommitted，那么我们可以看到save过的数据 session.save(user);//save后,马上发Hibernate: insert into tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

save后，将执行insert语句，返回有数据库生成的id



//纳入了session的管理，修改了session中existsInDatebase状态为true

mysql> select * from t_user2;

+---------+--------+----------+---------------------+---------------------+

| user_id | name | password | createtime | expiretime |

+---------+--------+----------+---------------------+---------------------+

| 1 | 猪八戒 | 123 | 2012-08-03 16:09:44 | 2012-08-03 16:09:55 |

+---------+--------+----------+---------------------+---------------------+

1 row in set (0.00 sec)

/** * 测试uuid主键生成策略2：先save后evict：抛出异常：org.hibernate.AssertionFailure: possible nonthreadsafe access to session */ publicvoid testSave3() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User1 user = new User1(); user.setName("王五"); user.setPassword("123"); user.setCreateTime(new Date()); user.setExpireTime(new Date()); //因为user的主键生成侧路采用的是uuid，所以调用完成save后，只是将user纳入到了session的管理 //不会发出insert语句，但是id已经生成，session中existsInDatebase状态为false session.save(user); //将user对象从session中逐出，即session的EntityEntries属性中逐出 session.evict(user); //无法成功提交，因为hibernate在清理缓存时，在session的insertions集合中取出user对象进行insert操作后 //需要更新entityEntries属性中的existsInDatabase为true，而我们采用evict已经将user从session的entityEntries //中逐出了，所以找不到相关数据，无法更新，抛出异常 tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

Save后：

Evict后：

org.hibernate.AssertionFailure: possible nonthreadsafe access to session

/** * 测试assigned主键生成策略:[注意使用的是每一张表t_user3] * */ publicvoid testSave6() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User3 user = new User3(); user.setId("001"); user.setName("张三"); session.save(user);[U1] user.setName("王五"); session.update[U2] (user); User3 user3 = new User3(); user3.setId("002"); user3.setName("李四"); session.save[U3] (user3); //Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?) //Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?) //Hibernate: update t_user3 set name=?, password=?, create_time=?, expire_time=? where user_id=? //hibernate按照save(insert),update、delete顺序提交相关操作 tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

//注意：hibernate按照save(insert),update、delete顺序提交相关操作

/** * 测试assigned主键生成策略:[注意使用的是每一张表t_user3] hibernate按照save(insert),update、delete顺序提交相关操作 * */ publicvoid testSave6() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User3 user = new User3(); user.setId("001"); user.setName("张三"); session.save(user); user.setName("王五"); session.update(user); User3 user3 = new User3(); user3.setId("002"); user3.setName("李四"); session.save(user3); //注意：hibernate按照save(insert),update、delete顺序提交相关操作 //Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?) //Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?) //Hibernate: update t_user3 set name=?, password=?, create_time=?, expire_time=? where user_id=? tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

Hibernate: update t_user3 set name=?, password=?, create_time=?, expire_time=? where user_id=?

mysql> select * from t_user3;

+---------+------+----------+-------------+-------------+

| user_id | name | password | create_time | expire_time |

+---------+------+----------+-------------+-------------+

| 001 | 王五 | NULL | NULL | NULL |

| 002 | 李四 | NULL | NULL | NULL |

+---------+------+----------+-------------+-------------+

2 rows in set (0.00 sec)

/** * 测试assigned主键生成策略:[注意使用的是每一张表t_user3]显示调用flush后，sql会按照我们的意愿执行 * */ publicvoid testSave7() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User3 user = new User3(); user.setId("003"); user.setName("张三"); session.save(user); user.setName("王五"); session.update(user); //因为我们在session.udpate(user)后执行了flush，所以在清理缓存时执行flush前的sql不会生成 //sql会按照我们的意愿执行 session.flush(); User3 user3 = new User3(); user3.setId("004"); user3.setName("李四"); session.save(user3); tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } } }

//Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

//Hibernate: update t_user3 set name=?, password=?, create_time=?, expire_time=? where user_id=?

//Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

Hibernate: update t_user3 set name=?, password=?, create_time=?, expire_time=? where user_id=?

Hibernate: insert into t_user3 (name, password, create_time, expire_time, user_id) values (?, ?, ?, ?, ?)

mysql> select * from t_user3;

+---------+------+----------+-------------+-------------+

| user_id | name | password | create_time | expire_time |

+---------+------+----------+-------------+-------------+

| 001 | 王五 | NULL | NULL | NULL |

| 002 | 李四 | NULL | NULL | NULL |

| 003 | 王五 | NULL | NULL | NULL |

| 004 | 李四 | NULL | NULL | NULL |

+---------+------+----------+-------------+-------------+

4 rows in set (0.00 sec)

不明白以下两个程序：

/** * 测试uuid主键生成策略3:先save后flush再evict[注意使用的是每一张表t_user1] */ publicvoid testSave4() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User1 user = new User1(); user.setName("王五"); user.setPassword("123"); user.setCreateTime(new Date()); user.setExpireTime(new Date()); //因为user的主键生成侧路采用的是uuid，所以调用完成save后，只是将user纳入到了session的管理 //不会发出insert语句，但是id已经生成，session中existsInDatebase状态为false session.save(user); //flush后hibernate会清理缓存，会将user对象保存到数据库中，将session中的insertions中的user对象 //清除，并且设置session中existsInDatebase的状态为true session.flush(); //将user对象从session中逐出，即session的EntityEntries属性中逐出 session.evict(user); //可以成功提交，因为hibernate在清理缓存时，在session的insertions集合中无法找到user对象 //所以就不会发出insert语句[U4] ，也不会更新session中的existsInDatabase的状态 tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

mysql> select * from t_user1;

+----------------------------------+---------+----------+---------------------+---------------------+

| user_id | name | password | create_time | expire_time |

+----------------------------------+---------+----------+---------------------+---------------------+

| 402881e738ebdb9f0138ebdcab230001 | 王五 | 123 | 2012-08-03 17:41:34 | 2012-08-03 17:41:35 |

| 402881e738ebe0960138ebe098920001 | 王五1 | 123 | 2012-08-03 17:46:01 | 2012-08-03 17:46:01 |

| 402881e738ebe5dc0138ebe5ddc10001 | 王五11 | 123 | 2012-08-03 17:51:46 | 2012-08-03 17:51:46 |

| 402881e738ebe6d60138ebe6d7b10001 | 王五111 | 123 | 2012-08-03 17:52:50 | 2012-08-03 17:52:50 |

+----------------------------------+---------+----------+---------------------+---------------------+

5 rows in set (0.00 sec)

/** * 测试native主键生成策略2:[注意使用的是每一张表t_user2] */ publicvoid testSave5() { Session session = null; Transaction tx = null; try { session = HibernateUtils.getSession(); tx = session.beginTransaction(); User2 user = new User2(); user.setName("张三11"); user.setPassword("123"); user.setCreateTime(new Date()); user.setExpireTime(new Date()); //因为user的主键生成策略为native,所以调用session.save后，将执行insert语句，返回有数据库生成的id //纳入了session的管理，修改了session中existsInDatebase状态为true //如果数据库的隔离级别设置为为提交读，那么我们可以看到save过的数据 session.save(user); //将user对象从session中逐出，即session的EntityEntries属性中逐出 session.evict(user); //可以成功提交，因为hibernate在清理缓存时，在session的insertions集合中无法找到user对象 //所以就不会发出[U5] insert语句，也不会更新session中的existsInDatabase的状态 tx.commit(); }catch(Exception e) { e.printStackTrace(); tx.rollback(); }finally { HibernateUtils.closeSession(session); } }

mysql> select * from t_user2;

+---------+---------+----------+---------------------+---------------------+

| user_id | name | password | createtime | expiretime |

+---------+---------+----------+---------------------+---------------------+

| 1 | 猪八戒 | 123 | 2012-08-03 16:09:44 | 2012-08-03 16:09:55 |

| 2 | 猪八戒2 | 123 | 2012-08-03 16:22:08 | 2012-08-03 16:22:08 |

| 3 | 张三11 | 123 | 2012-08-03 17:48:34 | 2012-08-03 17:48:35 |

| 4 | 张三111 | 123 | 2012-08-03 17:51:23 | 2012-08-03 17:51:23 |

| 5 | 张三1 | 123 | 2012-08-03 17:53:58 | 2012-08-03 17:53:58 |

+---------+---------+----------+---------------------+---------------------+

5 rows in set (0.00 sec)