JPA-抽象基实体类中的多对多关系和具体扩展实体子类中的联接表引用

Question

我有一个抽象的BaseEntity类，所有具体的entity类都是从它扩展的。

@Entity
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class BaseEntity implements Serializable {

    @Column(name = "uid")
    private Long uid;

    /** 
     * The owning side of a ManyToMany relationship from each entity to Tag
     */
    @ManyToMany(fetch = FetchType.EAGER)
    @JoinTable(name = "baseentity_tag", joinColumns =
    {
        @JoinColumn(name = "baseuid", referencedColumnName = "uid")
    }, inverseJoinColumns =
    {
        @JoinColumn(name = "taguid", referencedColumnName = "uid")
    })
    protected List<Tag> tags = new ArrayList<>();

    public Long getUid() {
        return uid;
    }

    public void setUid(Long uid) {
        this.uid = uid;
    }

    public void setTags(List<Tag> tags) {
        this.tags = tags;
    }

    public List<Tag> getTags() {
        return tags;
    }
}

@Entity
public class Tag extends BaseEntity {

    private static final long serialVersionUID = 1L;

    /** 
     * The inverse side of a ManyToMany relationship from Tag to each entity
     */
    @ManyToMany(mappedBy = "tags", fetch = FetchType.LAZY)
    private List<BaseEntity> baseEntities = new ArrayList<>();   

    public void setBaseEntities(List<BaseEntity> baseEntities) {
        this.baseEntities = baseEntities;
    }

    @XmlTransient
    public List<BaseEntity> getBaseEntities() {
        return baseEntities;
    }          
}

以上设计是否有问题；at线

@JoinColumn(name = "baseuid", referencedColumnName = "uid")

因为我希望连接表“baseentity_tag”（列“baseuid”）在每个具体实体类中都有引用，比如concrete1.java、concrete2.java等？

我想一个通用的连接表“baseEntity_tag”将不能满足所有具体实体的需要。

CREATE TABLE baseentity_tag (baseuid VARCHAR(255) NOT NULL, taguid BIGINT NOT NULL, PRIMARY KEY (baseuid, taguid));
ALTER TABLE baseentity_tag ADD CONSTRAINT FK_baseentity_tag_baseuid FOREIGN KEY (baseuid) REFERENCES conrete1 (uid);
ALTER TABLE baseentity_tag ADD CONSTRAINT FK_baseentity_tag_taguid FOREIGN KEY (taguid) REFERENCES tag (uid);

Answer 1

建立关系的方式与继承策略无关。因此，您的@manytomany关系的定义与关联的@jointable定义应该与所有可用的策略一起工作-single_table、jointed和table_per_class，所有这些策略都有不同的表集来支持策略。

在您的示例中，您选择了策略inheritanceType.table_per_class，因此您的每个具体类都有自己的表，其中包括从抽象超级baseEntity继承的字段。这些表中的每一个都包含一个UID列（tableTag)。这些具体类中的每一个都继承@ManyTomany关系，并引用可联合的baseEntity_tag，后者只是根据uid值链接实体。