java - Hibernate:带有继承的 NaturalId

Question

我有以下实体(简短版本):

学生组:

@Entity
@Table(name = "group_of_students")
@Inheritance(strategy = InheritanceType.JOINED)
public abstract class AGroupOfStudents extends AModel {
}

百人队:

@Entity
@Table(name = "cohort")
@PrimaryKeyJoinColumn(name = "id")
public class Cohort extends AGroupOfStudents {

    @Column(nullable = false)
    // @NaturalId <- here is the problem
    private int number;
}

队列:

@Entity
@Table(name = "centuria")
@PrimaryKeyJoinColumn(name = "id")
public class Centuria extends AGroupOfStudents {

    @Column(nullable = false)
    // @NaturalId <- here is the problem
    private int cohort;


    @Column(nullable = false)
    // @NaturalId <- here is the problem
    private char maniple;
}

所以我和一群学生一起进行类(class)讲座。有不同的学生组，例如 Centuria 或 Cohort。但我希望 Cohort 的数字字段是 NaturalId。这将导致错误:

AnnotationException: @NaturalId only valid on root entity (or its @MappedSuperclasses)

但是为什么我只能在根实体上使用@NaturalId？如何在不破坏类继承的情况下解决这个问题？

Answer 1

好吧，我完全误解了@NaturalId，主要目的是在表上启用此 NaturalId 的查询，因此这只适用于根实体才有意义。

想要的是我的子实体的简单唯一约束，这可以通过以下方式实现:

@Column(unique = true) 单列

@Table(name = "centuria", uniqueConstraints = { @UniqueConstraint(columnNames = { "cohort", "maniple", "letter"}) }) 对于多列