强制 JPA 从数据库重新加载实体 [英] Force JPA to reload entity from database

问题描述

我有一个 Foo 实体，它以一对一的关系链接到一个 Status 实体:

I have a Foo entity that's linked to a Status entity in a one-by-one relationship:

@Entity
@NamedQueries({
  @NamedQuery(name = "Foo.findById", query = "select o from Foo o where o.fooId = :fooId")
})
public class Foo implements Serializable {
    @Id
    @Column(name="FOO_ID")
    private Long fooId;

    @OneToOne(mappedBy = "foo")
    private Status status;

    public Long getFooId() {
        return fooId;
    }

    public void setFooId(Long fooId) {
        this.fooId = fooId;
    }

    public Status getStatus() {
        return status;
    }

    public void setStatus(Status status) {
        this.status = status;
    }
}

@Entity
public class FooCurrentStatus implements Serializable {
    @Id
    private Long fooId;

    @OneToOne
    @JoinColumn(name = "FOO_ID")
    private Foo foo;

    public Long getFooId() {
        return fooId;
    }

    public void setFooId(Long fooId) {
        this.fooId = fooId;
    }

    public Foo getFoo() {
        return foo;
    }

    public void setFoo(Foo foo) {
        this.foo = foo;
        if (foo != null) {
            this.fooId = foo.getFooId();
        }
    }
}

我明白这并非完全错误，因为当我获取 Foo 实例时，我会自动获取其状态.

I understand this is not completely wrong because when I fetch a Foo instance I automatically get its status.

从应用的角度来看，状态是只读的.它由其他一些修改数据库信息的无关进程在别处管理.

From the application point of view, the status is read-only. It is managed elsewhere, by some other unrelated process that modifies the database information.

不幸的是，副作用是每当状态发生变化时，我的托管实体就会过时.

Unfortunately, the side effect is that whenever the status changes my managed entity gets outdated.

如何指示 EJB/JPA 获取新状态?

How can I instruct EJB/JPA to grab a fresh status?

推荐答案

refresh() 专门用于此类用例，它可以强制刷新已从数据库加载实例的状态:

refresh() on the EntityManager API is particularly used for such use-case, which can force refreshing the state of an already loaded instance from the database:

entityManager.refresh(foo.getStatus());

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