即使没有调用persist，JPA / Hibernate也会保存

em.getTransaction().begin();

StringData sd = em.find(StringData.class, key);
System.out.println("Old value: " + sd.getData());
sd.setData(newValue);
// em.persist(sd);

em.getTransaction().commit();

正如您所看到的，我不会调用 persist ，它被注释掉了，因为我先干这个代码。然而，事实证明它并不是非常干燥。在检查数据库时，我发现数据发生了变化（幸运的是它是一个测试数据库）。

As you can see, I'm not calling persist, it's commented out, because I'm dry running this code first. However, as it turns out it's not so very dry. Upon inspecting the database, I see the data is changed (fortunately it's a test database).

显然，我对Hibernate / JPA的理解是有缺陷的。调用 persist 时总是需要更改数据吗？如果不是，什么时候什么规则保存了

Apparently my understanding of Hibernate/JPA is flawed. Isn't calling persist always required to change data? And if not, what are the rules on when something is saved?