20

问题

我想首先说我意识到数据库结构很糟糕，但我现在无法改变它。

话虽这么说，我需要在 Hibernate（4.2.1）中创建一个一对多的双向关系，它不涉及主键（只有关系的“父”端的唯一键）并且没有加入表。表示这种关系的外键是从“子”到“父”的反向指针（见下文）。我已经搜索并尝试了各种不同的注释配置，但没有成功。我要求的可能吗？

数据库

GLOBAL_PART

CREATE TABLE "GLOBAL_PART" (    
    "GLOBAL_PART_ID" NUMBER NOT NULL,
    "RELEASES" NUMBER,
    CONSTRAINT "GLOBAL_PART_PK" PRIMARY KEY ("GLOBAL_PART_ID"),
    CONSTRAINT "GLOBAL_PART_RELEASES_UK" UNIQUE ("RELEASES")
);

PART_RELEASE

CREATE TABLE "PART_RELEASE" (
    "PART_RELEASE_ID" NUMBER NOT NULL,
    "COLLECTION_ID" NUMBER,
    CONSTRAINT "PART_RELEASE_PK" PRIMARY KEY ("PART_RELEASE_ID"),
    CONSTRAINT "GLOBAL_PART_RELEASE_FK" FOREIGN KEY ("COLLECTION_ID")
        REFERENCES "GLOBAL_PART" ("RELEASES") ON DELETE CASCADE ENABLE
);

参考：

PART_RELEASE                 GLOBAL_PART
-------------------          ------------
PART_RELEASE_ID (PK)         GLOBAL_PART_ID (PK)
COLLECTION_ID -------------> RELEASES (UK)

爪哇

GlobalPart.java

@Entity
@Table(name = "GLOBAL_PART")
@SequenceGenerator(name = "SEQUENCE_GENERATOR", sequenceName = "GLOBAL_PART_SEQ")
public class GlobalPart extends ModelBase implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "GLOBAL_PART_ID", unique = true, nullable = false)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQUENCE_GENERATOR")
    private Long globalPartId;

    @OneToMany(fetch = FetchType.EAGER)
    @JoinColumn(name = "COLLECTIONGID")
    private Set<PartRelease> releases;

    public Long getGlobalPartId() {
        return globalPartId;
    }

    public void setGlobalPartId(Long globalPartId) {
        this.globalPartId = globalPartId;
    }

    public Set<PartRelease> getReleases() {
        return releases;
    }

    public void setReleases(Set<PartRelease> releases) {
        this.releases = releases;
    }

}

PartRelease.java

@Entity
@Table(name = "PART_RELEASE")
@SequenceGenerator(name = "SEQUENCE_GENERATOR", sequenceName = "PART_RELEASE_SEQ")
public class PartRelease extends ModelBase implements Serializable {

    private static final long serialVersionUID = 1L;

    @Id
    @Column(name = "PART_RELEASE_ID", unique = true, nullable = false)
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "SEQUENCE_GENERATOR")
    private String partReleaseId;

    @ManyToOne
    @JoinColumn(name = "RELEASES")
    private GlobalPart globalPart;

    public String getPartReleaseId() {
        return partReleaseId;
    }

    public void setPartReleaseId(String partReleaseId) {
        this.partReleaseId = partReleaseId;
    }

    public GlobalPart getGlobalPart() {
        return globalPart;
    }

    public void setGlobalPart(GlobalPart globalPart) {
        this.globalPart = globalPart;
    }

}

任何帮助将不胜感激！！

4

2 回答 2

41

首先，在双向关联中，始终存在定义映射的所有者侧和由mappedBy属性的存在标记的反向侧。

在 OneToMany 关联中，所有者方始终是多方（在您的情况下为 PartRelease）。

此外，默认情况下，连接列引用它所引用的实体的 ID。由于这不是您想要的，因此您必须指定引用的列名。

当然，必须映射 RELEASES 列：

public class GlobalPart extends ModelBase implements Serializable {

    @OneToMany(fetch = FetchType.EAGER, mappedBy = "globalPart")
    private Set<PartRelease> partReleases;

    @Column(name = "RELEASES")
    private Long releasesNumber;
}

public class PartRelease extends ModelBase implements Serializable {
    @ManyToOne
    @JoinColumn(name = "COLLECTION_ID", referencedColumnName = "RELEASES")
    private GlobalPart globalPart;

}

文档中很好地描述了关联。你应该阅读它。

于 2013-06-07T21:37:27.820 回答
2

每当您需要@ManyToOne在父端使用非主键列映射时，您必须使用注释的referencedColumnName属性。@JoinColumn

@ManyToOne(fetch = FetchType.LAZY)
@JoinColumn(
    name = "RELEASES", 
    referencedColumnName = "COLLECTIONGID"
)

我使用FetchType.LAZY了，@ManyToOne因为默认情况下FetchType.EAGER使用获取，这对性能非常不利。

于 2017-08-15T13:37:08.440 回答