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Spring Data 针对mongodb提供了乐观锁实现：
The @Version annotation provides syntax similar to that of JPA in the context of MongoDB and makes sure updates are only applied to documents with a matching version. Therefore,the actual value of the version property is added to the update query in such a way that the update does not have any effect if another operation altered the document in the meantime. In that case,an OptimisticLockingFailureException is thrown. The following example shows these features:
提供@Version注解，用来标识版本，保存、删除等操作会验证version，不一致会抛出OptimisticLockingFailureException
来看一个例子：
@Document
class Person {
@Id String id;
String firstname;
String lastname;
@Version Long version;
}
Person daenerys = template.insert(new Person("Daenerys")); (1)
Person tmp = template.findOne(query(where("id").is(daenerys.getId())),Person.class); (2)
daenerys.setLastname("Targaryen");
template.save(daenerys); (3)
template.save(tmp); // throws OptimisticLockingFailureException (4)
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最初插入一个person daenerys，version为0。
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加载刚插入的数据，tmp。version还是0。
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更新version = 0的daenerys，更新lastname，save后version变为1。
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现在来更新，会抛出OptimisticLockingFailureException， 提示操作失败。
注意：
| Important |
Optimistic Locking requires to set the?WriteConcern?to?ACKNOWLEDGED. Otherwise?OptimisticLockingFailureException?can be silently swallowed. |
| Note |
As of Version 2.2?MongoOperations?also includes the?@Version?property when removing an entity from the database. To remove a?Document?without version check use?MongoOperations#remove(Query,…?)?instead of?MongoOperations#remove(Object). |
| Note |
As of Version 2.2 repositories check for the outcome of acknowledged deletes when removing versioned entities. An?OptimisticLockingFailureException?is raised if a versioned entity cannot be deleted through?CrudRepository.delete(Object). In such case,the version was changed or the object was deleted in the meantime. Use?CrudRepository.deleteById(ID)?to bypass optimistic locking functionality and delete objects regardless of their version. |
作者：Jadepeng
出处：jqpeng的技术记事本--http://www.cnblogs.com/xiaoqi
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