JPA/Hibernate:@ManyToOne和@OneToOne关系被标记为FetchType.LAZY,而Optional = false不能在em.find()上懒惰加载？

Question

我有以下实体(仅显示相关映射):

@Entity
@Table(name = "PQs")
public class PQ implements Serializable
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column
    private Integer id;

    @Column
    private String name;

    @ManyToOne(fetch = FetchType.LAZY)                 // lazy XToOne
    @JoinColumn(name = "user_id", referencedColumnName = "person_id")
    private User user;

    @OneToOne(mappedBy = "pq", fetch = FetchType.LAZY) // lazy XToOne
    private Group group;

    @OneToOne(mappedBy = "pq", fetch = FetchType.LAZY) // lazy XToOne
    private Tendering tendering;

    ...
}

请注意上面的注释:@XToOne与其他实体有三种关系:

用户(具有简单ID作为PK的SecurityIdentity子类,由PQ表示所有者):

@Entity
@Table(name = "Users")
@DiscriminatorValue(value = "user")
public class User extends SecurityIdentity
{
    @Column
    private String name;

    @OneToMany(mappedBy = "user")
    private Set<PQ> pqs = new HashSet<PQ>();

    ...
}

组(也是具有简单ID作为PK的SecurityIdentity子类,引用PQ来表示可以与该PQ交互的一组用户):

@Entity
@Table(name = "Groups")
@DiscriminatorValue(value = "group")
public class Group extends SecurityIdentity
{
    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "pq_id", referencedColumnName = "id")
    private PQ pq;

    ...
}

招标:

@Entity
@Table(name = "Tenderings")
public class Tendering implements Serializable
{
    @Id
    @Column(name = "pq_id", insertable = false, updatable = false)
    private Integer pqId;

    @Column(name = "external_code")
    private String externalCode;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "pq_id", referencedColumnName = "id")
    private PQ pq;

    ...
}

不要对共享ID的组和用户感到困惑,只需将它们视为简单ID即可.招标只是一个单独的文档对象(一对一).

正如您所看到@XToOne的,PQ实体上有三种关系,如果没有设置提取类型,则会急切加载(JPA默认值).所以为了防止这种情况,我将所有@XToOne关系标记为FetchType.LAZY.

现在使用时

em.find(PQ.class, someExistingId);

我得到了Hibernate输出:

23:53:55,815 INFO  [stdout] Hibernate: select pq0_.id as id291_0_, pq0_.description as descript2_291_0_, pq0_.name as name291_0_, pq0_.submission_date as submission4_291_0_, pq0_.user_id as user5_291_0_ from PQs pq0_ where pq0_.id=?
23:53:55,818 INFO  [stdout] Hibernate: select user0_.id as id280_0_, user0_1_.identity_type_id as identity2_280_0_, user0_.is_enabled as is1_297_0_, user0_.name as name297_0_, user0_.password as password297_0_, user0_.person_id as person5_297_0_ from Users user0_ inner join SecurityIdentities user0_1_ on user0_.id=user0_1_.id where user0_.person_id=?
23:53:55,821 INFO  [stdout] Hibernate: select group0_.id as id280_0_, group0_1_.identity_type_id as identity2_280_0_, group0_.pq_id as pq2_281_0_ from Groups group0_ inner join SecurityIdentities group0_1_ on group0_.id=group0_1_.id where group0_.pq_id=?
23:53:55,823 INFO  [stdout] Hibernate: select tendering0_.pq_id as pq1_296_0_, tendering0_.binary_file as binary2_296_0_, tendering0_.customer_id as customer6_296_0_, tendering0_.description as descript3_296_0_, tendering0_.external_code as external4_296_0_, tendering0_.title as title296_0_ from Tenderings tendering0_ where tendering0_.pq_id=?

另外三个SELECT来自@XToOne关系(如网上许多地方所述).我看到的来源主要是这样的:

使OneToOne关系变得懒惰

如前所述,不应该提取这种@ManyToOne关系User user:

@ManyToOne(fetch=FetchType.LAZY) 应该工作得很好.

...这里的关系从PQ到用户,但它是牵强,因为你可以在看到select user0_.id as id280_0_, ...声明...

对于其他两个Group group和Tendering tendering两个@OneToOne 反向映射,外键引用PQ表的PK(ID),从而在PQ实体中产生相同的映射.

请注意,所有三个关系都不是可选的:PQ始终具有所有者(用户),并且PQ始终由招标和组实体引用.我刚才没有在上面的JPA中建模......

因此,当添加optional = false到PQ实体的三个关系时:

@Entity
@Table(name = "PQs")
public class PQ implements Serializable
{
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column
    private Integer id;

    @Column
    private String name;

    @ManyToOne(fetch = FetchType.LAZY, optional = false)
    @JoinColumn(name = "user_id", referencedColumnName = "person_id")
    private User user;

    @OneToOne(mappedBy = "pq", fetch = FetchType.LAZY, optional = false)
    private Group group;

    @OneToOne(mappedBy = "pq", fetch = FetchType.LAZY, optional = false)
    private Tendering tendering;

    ...
}

...我得到以下Hibernate输出:

00:47:34,397 INFO  [stdout] Hibernate: select pq0_.id as id361_0_, pq0_.description as descript2_361_0_, pq0_.name as name361_0_, pq0_.submission_date as submission4_361_0_, pq0_.user_id as user5_361_0_ from PQs pq0_ where pq0_.id=?
00:47:34,410 INFO  [stdout] Hibernate: select user0_.id as id350_0_, user0_1_.identity_type_id as identity2_350_0_, user0_.is_enabled as is1_367_0_, user0_.name as name367_0_, user0_.password as password367_0_, user0_.person_id as person5_367_0_ from Users user0_ inner join SecurityIdentities user0_1_ on user0_.id=user0_1_.id where user0_.person_id=?
00:47:34,413 INFO  [stdout] Hibernate: select group0_.id as id350_0_, group0_1_.identity_type_id as identity2_350_0_, group0_.pq_id as pq2_351_0_ from Groups group0_ inner join SecurityIdentities group0_1_ on group0_.id=group0_1_.id where group0_.pq_id=?

请注意,我只是optional = false在PQ实体上玩,因为这是我使用的那个em.find(...).(如果这还不够,请赐教.)

我现在的问题是双重的:

1. 为什么@ManyToOne对该User实体的热切期望(鉴于据说这是懒惰的工作,请参阅使一个OneToOne关系变得懒惰)？
2. 为什么只有实体的OneToOne关系Tendering不被提取？是因为Tendering实体引用PQ的PK列作为PK本身(@Idin Tendering),Group实体没有(与PQ的PK有规律关系)？

怎么了？如何使这些非可选关系变得懒惰？(没有代码检测或其他黑客,只是简单的注释......)

我知道LAZY的事情只是提示JPA提供者做一些关于延迟加载的事情,但是在这种情况下,好像其他东西是错误的(因为它的一部分是有效的).

PS:我正在使用Hibernate 4.0 BETA,JBoss 7.0.0.Final附带的版本以及JPA注释(以上都是JPA 1.0兼容).

Answer 1

您好，我不确定 JPA，但是对于many-to-one和one-to-one映射，hibernate 支持的惰性值是proxy，no-proxy其中false默认为 false 。检查 DTD 的这一部分

lazy="proxy|no-proxy|false"

你可以检查这个链接。我认为这在很大程度上回答了你的第一个问题。