EJB3持久性NamedQuery中的LockMode

问题描述

我们如何在EJB3持久性NamedQuery中指定LockMode?我想将Pessimistic LockMode添加到我现有的选择中，以便我可以在必要时进行更新，但是令人惊讶的是，查询对象没有setLockMode(xxx)方法(我的理解是，如果JPA是EJB3持久性的子集，则公开setLockMode，EJB3持久性应该具有可用的方法也).

How do we specify LockMode in EJB3 Persistence NamedQuery? I want to add Pessimistic LockMode to my existing select so that I can update if necessary but surprisingly Query object doesnot have setLockMode(xxx) method ( My understanding was if JPA, asubset of EJB3 persistence, exposes setLockMode, EJB3 persistence should have the method available too).

Query query = em.createNamedQuery("findOptoutStudent");
query.setParameter("optoutIndicator", optoutIndicator);
List<Student> students = query.getResultList();
return students.get(0);

我认为我不必手动将查询更改为选择更新".

I would assume I dont have to change the query manually to "select for update".

谢谢凯文

推荐答案

悲观锁定模式:

• PESSIMISTIC_READ表示共享锁.当另一个实体管理器获取PESSIMISTIC_WRITE时，锁定请求失败.

• PESSIMISTIC_READ which represents a shared lock. Lock request fails when another entity manager has acquired PESSIMISTIC_WRITE.

PESSIMISTIC_WRITE表示排他锁.当另一个实体管理器获取了对象上的任何一个锁时，锁请求将失败.

PESSIMISTIC_WRITE which represents an exclusive lock. Lock request fails when another entity manager has acquired either of the locks on the object.

在对象上应用锁定

entityManager.lock(object, LockModeType.PESSIMISTIC_READ)

随后释放锁

entityManager.lock(object, LockModeType.NONE)

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