java 使用 JPA 的表排他锁
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Table exclusive lock with JPA
提问by Radek Posto?owicz
Is it possible to lock exclusively entire table with JPA in database agnostic way (without using native queries for instance)? So far I saw only EntityManager.lock(*)but this locks only given record.
是否可以以数据库不可知的方式使用 JPA 锁定整个表（例如，不使用本机查询）？到目前为止，我只看到了EntityManager.lock(*)这个锁只给出了记录。
回答by OndroMih
I don't think this is supported by JPA natively - you always lock single entity or every entity which is a result from a query. Inserts are always allowed as they are new entities. You may either use native query to trigger a lock using SQL supported by your DB server, or you need to lock your insert programmatically.
我认为 JPA 本身不支持这 - 您总是锁定单个实体或每个查询结果的实体。始终允许插入，因为它们是新实体。您可以使用数据库服务器支持的 SQL 使用本机查询来触发锁定，或者您需要以编程方式锁定您的插入。
By programmatically I mean that you need to acquire a lock before every insert. You may do it by creating a separate lock entity class, each entity for a table you want to lock, and then before each insert, you lock particular entity with a read lock like this:
以编程方式我的意思是你需要在每次插入之前获取一个锁。您可以通过创建一个单独的锁定实体类来实现，每个实体都用于要锁定的表，然后在每次插入之前，使用读取锁锁定特定实体，如下所示：
em.createQuery("select l from TableLock l where l.entity = :entityName", TableLock.class)
.setParameter("entityName", MyEntity.class.getSimpleName())
.setLockMode(LockModeType.PESSIMISTIC_READ)
.getResultList();
em.persist(new MyEntity());
Of course, you should also check if the lock entity exists in database, and if not, create it first, with entity field being the name of your entity.
当然，您还应该检查数据库中是否存在锁定实体，如果不存在，请先创建它，实体字段为您的实体名称。
