JPA最佳实践:静态查找实体。

Imagine, an Event entity references a Status Entity:

想象一下，一个事件实体引用一个状态实体:

@Entity
@Table(name = "event")
public class Event()
{
  @Id
  @Column(name = "id", nullable = false)
  private long id;
  ...

  @ManyToOne
  @JoinColumn(name = "status_code", nullable = false)
  private Status status;
}


@Entity
@Table(name = "status")
public class Status()
{
  @Id
  @Column(name = "code", nullable = false)
  private String code;

  @Column(name = "label", nullable = false, updatable = false)
  private String label;
}

Status is mapped to a small table 'status'. Status is a typical reference data / lookup Entity.

状态映射到一个小表“Status”。状态是一个典型的引用数据/查找实体。

   code  label
   ----- --------------
   CRD   Created
   ITD   Initiated
   PSD   Paused
   CCD   Cancelled
   ABD   Aborted

I'm not sure if it is a good idea to model Status as an Entity. It feels more like an enumeration of constants...

我不确定将状态建模为实体是否是一个好主意。它更像是对常量的枚举……

By mapping Status as an Entity, I can use Status objects in Java code, and the Status values are equally present in the database. This is good for reporting.

通过将状态映射为实体，我可以在Java代码中使用状态对象，并且状态值在数据库中同样存在。这有利于报道。

On the other hand, if I want to set a particular Status to an Event, I can't simply assign the constant status I have in mind. I have to lookup the right entity first:

另一方面，如果我想为一个事件设置一个特定的状态，我不能简单地分配我心中的常量状态。我必须先查找正确的实体:

event.setStatus(entityManager.find(Status.class, "CRD"))

Can I avoid the above code fragment? I'm affraid for a performance penalty and it looks very heavy...

我可以避免上面的代码片段吗?我很害怕被罚点球，看起来很重……

Do I have to tweak things with read-only attributes?
我需要对具有只读属性的东西进行调整吗?
Can I prefetch these lookup entities and use them as constants?
我可以预取这些查找实体并将它们作为常量使用吗?
Did I miss a crucial JPA feature?
我是否错过了一个关键的JPA特性?
...?
……?

All opinions / suggestions / recommendations are welcome!

欢迎提出意见/建议!

Thank you! J.

谢谢你！J。

2 个解决方案

#1

Can I avoid the above code fragment? I'm affraid for a performance penalty and it looks very heavy?

我可以避免上面的代码片段吗?我被判罚款，而且看起来很重?

Well, you could use an enum instead. I don't really see why you don't actually.

你可以用enum代替。我不明白你为什么不。

But if you really want to use an entity, then it would be a perfect candidate for 2nd level caching and this would solve your performance concern.

但是如果您真的想要使用实体，那么它将是二级缓存的理想候选，这将解决您的性能问题。

#2

You could use entityManager.getReference(Status.class, "CRD"), which might not fetch the entity from the database if it is only used to set a foreign key.

您可以使用entityManager.getReference(状态。类“CRD”)，如果实体只用于设置外键，则它可能不会从数据库中获取实体。

#1