JPA合并与持久性 [英] JPA merge vs. persist

问题描述

到目前为止，我一直希望始终使用EntityManager的 merge（）来处理插入和更新。但我也注意到merge在update / insert之前执行了额外的select查询，以确保数据库中不存在记录。

So far, my preference has been to always use EntityManager's merge() take care of both insert and update. But I have also noticed that merge performs an additional select queries before update/insert to ensure record does not already exists in the database.

现在我正在处理一个项目需要对数据库进行大量（批量）插入。从性能的角度来看，在我绝对知道我总是创建一个要保留的对象的新实例的场景中使用persist而不是merge是有意义的吗？

Now that I am working on a project requiring extensive (bulk) inserts to the database. From a performance point of view does it make sense to use persist instead of merge in a scenario where I absolutely know that I am always creating a new instance of objects to be persisted?

推荐答案

当 persist 足够时，使用 merge 并不是一个好主意 - merge 做了相当多的工作。该主题之前已经在StackOverflow上讨论过，并且这篇文章详细解释了这些差异，并带来了一些不错的流程图表使事情变得清晰。

It's not a good idea using merge when a persist suffices - merge does quite a lot more of work. The topic has been discussed on StackOverflow before, and this article explains in detail the differences, with some nice flow diagrams to make things clear.

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