EntityManager在查询后不刷新数据 [英] EntityManager doesn't refresh the data after querying

问题描述

我当前的项目使用HSQLDB2.0和JPA2.0.

My current project uses HSQLDB2.0 and JPA2.0 .

方案是:我查询数据库以获取person的contactDetails的列表.我在用户界面上删除了一个contactInfo，但不保存该数据(取消保存部分).

The scenario is: I query DB to get list of contactDetails of person. I delete single contactInfo at UI but do not save that data (Cancel the saving part).

我再次执行相同的查询，现在结果列表比以前的结果小1，因为我在UI上删除了一个contactInfo.但是，如果我进行交叉检查，该contactInfo在DB上仍然可用.

I again do the same query, now the result list is 1 lesser than previous result coz I have deleted one contactInfo at UI. But that contactInfo is still available at DB if I cross check.

但是，如果我在查询开始前加入entityManager.clear()，则每次都会得到正确的结果.

But if I include entityManager.clear() before start of the query, I get correct results every time.

我不了解这种行为.有人可以为我说清楚吗?

I dont understand this behaviour. Could anyone make it clear for me?

推荐答案

而不是再次查询，请尝试以下操作:

Rather than querying again, try this:

entityManager.refresh(person);

更完整的示例:

EntityManagerFactory factory = Persistence.createEntityManagerFactory("...");
EntityManager em = factory.createEntityManager();
em.getTransaction().begin();

Person p = (Person) em.find(Person.class, 1);
assertEquals(10, p.getContactDetails().size()); // let's pretend p has 10 contact details
p.getContactDetails().remove(0);
assertEquals(9, p.getContactDetails().size());

Person p2 = (Person) em.find(Person.class, 1);
assertTrue(p == p2); // We're in the same persistence context so p == p2
assertEquals(9, p.getContactDetails().size());

// In order to reload the actual patients from the database, refresh the entity
em.refresh(p);
assertTrue(p == p2);
assertEquals(10, p.getContactDetails().size());
assertEquals(10, p2.getContactDetails().size());

em.getTransaction().commit();
em.close();
factory.close();

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