entity manager

基本解释

To have persistence actions, you need an entity manager.
要具有持久操作，您需要一个实体管理器。
They should be ready for invocation in any tier, whether within the realm of the entity manager or not.
无论是否在实体管理器中，它们都应该准备好在任何层中调用。
Another restriction arises from the fact that the domain objects can be accessed both in the tier where they are managed by the entity manager and in all the other tiers where they are detached.
另一种限制源自于这样一个事实：域对象可以通过由实体管理器所管理的域对象所在的层访问，也可以通过分离它的所有其他层访问。