如何锁定表...做些什么...用Spring Boot解锁表?

问题描述

该想法基本上是为了扩展具有自定义功能的 some 存储库.所以我得到了这个设置，它可以工作！

The idea is basically to extend some Repositories with custom functionality. So I got this setup, which DOES work!

@MappedSuperclass
abstract class MyBaseEntity {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    var id: Int = 0

    var eid: Int = 0

}

interface MyRepository<T : MyBaseEntity> {

    @Transactional
    fun saveInsert(entity: T): Optional<T>
}

open class MyRepositoryImpl<T : MyBaseEntity> : MyRepository<T> {

    @Autowired
    private lateinit var entityManager: EntityManager

    @Transactional
    override fun saveInsert(entity: T): Optional<T> {

        // lock table
        entityManager.createNativeQuery("LOCK TABLE myTable WRITE").executeUpdate()

        // get current max EID
        val result = entityManager.createNativeQuery("SELECT MAX(eid) FROM myTable LIMIT 1").singleResult as? Int ?: 0

        // set entities EID with incremented result
        entity.eid = result + 1

        // test if table is locked. sending manually 2-3 POST requests to REST
        Thread.sleep(5000)

        // save
        entityManager.persist(entity)

        // unlock
        entityManager.createNativeQuery("UNLOCK TABLES").executeUpdate()

        return Optional.of(entity)
    }
}

我该如何像春季一样?

起初，我以为@Transactional会执行LOCK和UNLOCK任务.我尝试了几个其他参数和@Lock.我确实阅读了文档和一些教程，但是抽象的技术英语通常不容易理解.最后，我没有一个可行的解决方案，所以我手动添加了表锁定，效果很好.仍然希望采用一种更像弹簧的方式.

At first, I thought the @Transactional would do the LOCK and UNLOCK stuff. I tried a couple of additional parameters and @Lock. I did go through docs and some tutorials but the abstract technical English is often not easy to understand. At the end, I did not get a working solution so I manually added the table-locking, which works fine. Still would prefer a more spring-like way to do it.

推荐答案

1)您当前的设计也可能有问题. persist不会立即在数据库中插入一行.当方法返回时，在事务提交时会发生这种情况.

1) There might be a problem with your current design as well. The persist does not instantly INSERT a row in the database. That happens on transaction commit when the method returns.

因此您可以在实际插入之前解锁表:

So you unlock the table before the actual insert:

    // save
    entityManager.persist(entity) // -> There is no INSERT at this point.

    // unlock
    entityManager.createNativeQuery("UNLOCK TABLES").executeUpdate()

2)返回到仅使用不带本机的JPA的操作方法(由于默认情况下不支持，因此仍需要一些解决方法):

2) Going back to how to do it only with JPA without natives (it still requires a bit of a workaround as it is not supported by default):

    // lock table by loading one existing entity and setting the LockModeType
    Entity lockedEntity = entityManager.find(Entity.class, 1, LockModeType.PESSIMISTIC_WRITE);

    // get current max EID, TRY NOT TO USE NATIVE QUERY HERE

    // set entities EID with incremented result

    // save
    entityManager.persist(entity)
    entityManager.flush() // -> Force an actual INSERT

    // unlock by passing the previous entity
    entityManager.lock(lockedEntity, LockModeType.NONE)

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