休眠多对一关系，不带主键或联接表

java one-to-many hibernate

2022-09-02 09:03:44

问题

我想首先说，我意识到数据库结构是残酷的，但我现在无法改变它。

话虽如此，我需要在Hibernate（4.2.1）中创建一个一对多的双向关系，该关系不涉及主键（仅涉及关系的“父”端的唯一键）和连接表。表示此关系的外键是从“子”到“父”的后退点（见下文）。我已经搜索并尝试了各种不同的注释配置，但没有运气。我所要求的可能吗？

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)

爪哇岛

全球部分.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;
    }

}

部件发布.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！

答案 1

首先，在双向关联中，总是有一个所有者端，它定义了映射，还有一个逆端，由属性的存在来标记。mappedBy

在OneToMany协会中，所有者一方始终是多方（在您的情况下，PartRelease）。

此外，默认情况下，联接列引用它所引用的实体的 ID。由于它不是您想要的，因此必须指定引用的列名称。

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。

答案 2

每当需要使用父端的非主键列映射@ManyToOne时，都必须使用批注的属性。referencedColumnName@JoinColumn

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

我之所以使用，是因为默认情况下，使用 FetchType.EAGER fetching，这对性能非常不利。FetchType.LAZY@ManyToOne