EntityManager.flush做了什么以及为什么需要使用它？ [英] What does EntityManager.flush do and why do I need to use it?

问题描述

我有一个EJB，我将对象保存到数据库。在我看到的一个例子中，一旦保存了这个数据（EntityManager.persist），就会调用EntityManager.flush（）;为什么我需要这样做？我保存的对象没有附加，以后不会在方法中使用。事实上，一旦保存，方法返回，我希望资源被释放。 （示例代码也会在删除调用中执行此操作。）

I have an EJB where I am saving an object to the database. In an example I have seen, once this data is saved (EntityManager.persist) there is a call to EntityManager.flush(); Why do I need to do this? The object I am saving is not attached and not used later in the method. In fact, once saved the method returns and I would expect the resources to be released. (The example code does this on a remove call as well.)

if (somecondition) {
    entityManager.persist(unAttachedEntity);
} else {
    attachedEntityObject.setId(unAttachedEntity.getId());
}
entityManager.flush();

推荐答案

调用 EntityManager。 flush（）; 将强制数据立即在数据库中持久存在，因为 EntityManager.persist（）不会（取决于EntityManager的工作方式）配置： FlushModeType （AUTO或COMMIT）默认设置为AUTO和a flush将自动完成，如果它被设置为COMMIT，那么当提交事务时，数据的持久性将被延迟。

A call to EntityManager.flush(); will force the data to be persist in the database immediately as EntityManager.persist() will not (depending on how the EntityManager is configured : FlushModeType (AUTO or COMMIT) by default it's set to AUTO and a flush will be done automatically by if it's set to COMMIT the persitence of the data to the underlying database will be delayed when the transaction is commited).

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