java - 如何在 "manual"后端查询更新后刷新实体

Question

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Answer 1

If I make a simple Respository.findOne(objectId) I get old object (not updated one). I've to call Entitymanager.refresh(object) to get updated object.

Why?

一级缓存在 session 期间处于 Activity 状态。除非有理由返回数据库，否则将从一级缓存中检索先前在 session 上下文中检索到的任何对象实体。

在 SQL 更新后是否有返回数据库的原因？好吧，正如 Pro JPA 2 书中关于批量更新语句(通过 JPQL 或 SQL)的注释 (p199):

The first issue for developers to consider when using these [bulk update] statements is that the persistence context is not updated to reflect the results of the operation. Bulk operations are issued as SQL against the database, bypassing the in-memory structures of the persistence context.

这就是你所看到的。这就是为什么您需要调用刷新以强制从数据库重新加载实体，因为持久性上下文不知道任何潜在的修改。

本书还对使用 Native SQL 语句(而不是 JPQL 批量更新)做了如下说明:

■ CAUTION Native SQL update and delete operations should not be executed on tables mapped by an entity. The JP QL operations tell the provider what cached entity state must be invalidated in order to remain consistent with the database. Native SQL operations bypass such checks and can quickly lead to situations where the inmemory cache is out of date with respect to the database.

从本质上讲，如果您配置了二级缓存，那么通过 native SQL 语句更新当前缓存中的任何实体可能会导致缓存中的数据过时。