hibernate异常 org.hibernate.StaleObjectStateException: Row was updated or deleted
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Hibernate支持乐观锁。当多个事务同时对数据库表中的同一条数据操作时,如果没有加锁机制的话,就会产生脏数据(duty data)。Hibernate有2种机制可以解决这个问题:乐观锁和悲观锁。这里我们只讨论乐观锁。
Hibernate乐观锁,能自动检测多个事务对同一条数据进行的操作,并根据先胜原则,提交第一个事务,其他的事务提交时则抛出org.hibernate.StaleObjectStateException异常。
Hibernate乐观锁是怎么做到的呢?
我们先从Hibernate乐观锁的实现说起。
要实现Hibenate乐观锁,我们首先要在数据库表里增加一个版本控制字段,字段名随意,比如就叫version,对应hibernate类型只能为long,integer,short,timestamp,calendar,也就是只能为数字或timestamp类型。然后在hibernate mapping里作如下类似定义:
告诉Hibernate version作为版本控制用,交由它管理。
当然在entity class里也需要给version加上定义,定义的方法跟其他字段完全一样。
Hibernate乐观锁的的使用:
在事务2提交时,因为它提交的数据比事务1提交后的数据旧,所以hibernate会抛出一个org.hibernate.StaleObjectStateException异常。
回到前面的问题,Hibernate怎么知道事务2提交的数据比事务1提交后的数据旧呢?
因为MyEntity有个version版本控制字段。
回头看看上面的源代码中的:
MyEntity et1 = session1.load(MyEntity.class, id);
MyEntity et2 = session2.load(MyEntity.class, id);
这里,et1.version==et2.version,比如此时version=1,
当事务1提交后,该数据的版本控制字段version=version+1=2,而事务2提交时version=1<2所以Hibernate认为事务2提交的数据为过时数据,抛出异常。
这就是Hibernate乐观锁的原理机制。
我们已经知道了Hibernate乐观锁是根据version的值来判断数据是否过时,也就是说,在向数据库update某数据时,必须保证该entity里的version字段被正确地设置为update之前的值,否则hibernate乐观锁机制将无法根据version作出正确的判断。
在我们的WEB应用中,尤其应该注意这个问题。
Hibernate乐观锁是怎么做到的呢?
我们先从Hibernate乐观锁的实现说起。
要实现Hibenate乐观锁,我们首先要在数据库表里增加一个版本控制字段,字段名随意,比如就叫version,对应hibernate类型只能为long,integer,short,timestamp,calendar,也就是只能为数字或timestamp类型。然后在hibernate mapping里作如下类似定义:
- <version name="version"
- column="VERSION"
- type="integer"
- />
告诉Hibernate version作为版本控制用,交由它管理。
当然在entity class里也需要给version加上定义,定义的方法跟其他字段完全一样。
- private Integer version;
- …
- // setVersion() && getVersion(Integer)
Hibernate乐观锁的的使用:
- <DIV class=tf_edit_html_lineno id=tf_edit_html_lineno><SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">1</SPAN>Session session1 = sessionFactory.openSession();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">2</SPAN>Session session2 = sessionFactory.openSession();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">3</SPAN>
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">4</SPAN>MyEntity et1 = session1.load(MyEntity.class, id);
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">5</SPAN>MyEntity et2 = session2.load(MyEntity.class, id);
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">6</SPAN>//这里 et1, et2为同一条数据
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">7</SPAN>
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">8</SPAN>Transaction tx1 = session1.beginTransaction();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">9</SPAN>//事务1开始
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">10</SPAN>et1.setName(“Entity1”);
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">11</SPAN>//事务1中对该数据修改
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">12</SPAN>
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">13</SPAN>tx1.commit();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">14</SPAN>session1.close();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">15</SPAN>//事务1提交
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">16</SPAN>
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">17</SPAN>Transaction tx2 = session2.beginTransaction();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">18</SPAN>//事务2开始
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">19</SPAN>et2.setName(“Entity2”);
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">20</SPAN>//事务2中对该数据修改
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">21</SPAN>
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">22</SPAN>tx2.commit();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">23</SPAN>session2.close();
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">24</SPAN>//事务2提交
- <SPAN style="PADDING-RIGHT: 3px; WIDTH: 1.5em; COLOR: #aaaadd; FONT-FAMILY: verdana">25</SPAN>
- </DIV>
在事务2提交时,因为它提交的数据比事务1提交后的数据旧,所以hibernate会抛出一个org.hibernate.StaleObjectStateException异常。
回到前面的问题,Hibernate怎么知道事务2提交的数据比事务1提交后的数据旧呢?
因为MyEntity有个version版本控制字段。
回头看看上面的源代码中的:
MyEntity et1 = session1.load(MyEntity.class, id);
MyEntity et2 = session2.load(MyEntity.class, id);
这里,et1.version==et2.version,比如此时version=1,
当事务1提交后,该数据的版本控制字段version=version+1=2,而事务2提交时version=1<2所以Hibernate认为事务2提交的数据为过时数据,抛出异常。
这就是Hibernate乐观锁的原理机制。
我们已经知道了Hibernate乐观锁是根据version的值来判断数据是否过时,也就是说,在向数据库update某数据时,必须保证该entity里的version字段被正确地设置为update之前的值,否则hibernate乐观锁机制将无法根据version作出正确的判断。
在我们的WEB应用中,尤其应该注意这个问题。
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