Question

我在我申请的网上信标层中有一个日本邮局实体。如果该实体在数据库中已经存在,或只在用户会议上存在,我随时想知道。

这将是在业务层面,我将使用实体经理(实体)方法,但我认为,在我的核心层次上,我需要一个额外特性,表明该实体是否得到拯救。如何执行? 现在考虑以下选择:

a JPA attribute with a default value set by the database, but would force a new read after each update ?
a non JPA attribute manually set in my code or automatically set by JPA?

任何建议或其他建议?

I m使用JPA 1,Hibernate 3.2 执行,倾向于遵守标准。

Answer 1

首先,请提醒各国注意一个实体。从JPA 1.0规格(第3.2节,实体生活周期):

This section describes the EntityManager operations for managing an entity instance’s lifecycle. An entity instance may be characterized as being new, managed, detached, or removed.

A new entity instance has no persistent identity, and is not yet associated with a persistence context.

A managed entity instance is an instance with a persistent identity that is currently associated with a persistence context.

A detached entity instance is an instance with a persistent identity that is not (or no longer) associated with a persistence context.

A removed entity instance is an instance with a persistent identity, associated with a persistence context, that is scheduled for removal from the database.

图表说明:

“alt

因此,根据定义,一个脱离实体已经存在,我实际上并不认为这是你的真正问题。现在,如果你想要知道一个实体是new(即没有固定身份),那么这方面的情况是:

@Transient
public boolean isNew() {
    return (this.id == null);
}

友情链接