java - Hibernate，单表继承和使用父类(super class)字段作为鉴别器列

Question

我有以下几种用于 hibernate 实体层次结构的类。我正在尝试拥有两个具体的子类 Sub1Class 和 Sub2Class。它们由 MappedSuperClass 中定义的鉴别器列(field)分隔。有一个抽象实体类 EntitySuperClass 被其他实体引用。其他实体不应该关心它们实际上是在引用 Sub1Class 还是 Sub2Class。

这真的可能吗？目前我收到此错误(因为列定义在 Sub1Class 和 EntitySuperClass 中被继承了两次):

Repeated column in mapping for entity: my.package.Sub1Class column: field (should be mapped with insert="false" update="false")

如果我将 @MappedSuperClass 添加到 EntitySuperClass，那么我会从 hiberante 得到断言错误:如果一个类既是 Entity 又是映射的父类(super class)，它不喜欢。如果我从 EntitySuperClass 中删除 @Entity，则该类不再是实体并且不能从其他实体引用:

MappedSuperClass 是外部包的一部分，因此如果可能，不应更改它。

我的类(class):

@MappedSuperclass
public class MappedSuperClass {
    private static final String ID_SEQ = "dummy_id_seq";
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = ID_SEQ)
    @GenericGenerator(name=ID_SEQ, strategy="sequence")

    @Column(name = "id", unique = true, nullable = false, insertable = true, updatable = false)
    private Integer id;

    @Column(name="field", nullable=false, length=8)
    private String field;

    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getField() {
        return field;
    }
    public void setField(String field) {
        this.field = field;
    }
}


@Entity
@Table(name = "ACTOR")
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="field", discriminatorType=DiscriminatorType.STRING)
abstract public class EntitySuperClass extends MappedSuperClass {


    @Column(name="description", nullable=false, length=8)
    private String description;

    public String getDescription() {
        return description;
    }

    public void setDescription(String description) {
        this.description = description;
    }
}

@Entity
@DiscriminatorValue("sub1")
public class Sub1Class extends EntitySuperClass {

}


@Entity
@DiscriminatorValue("sub2")
public class Sub2Class extends EntitySuperClass {

}


@Entity
public class ReferencingEntity {
    @Id
    @GeneratedValue(strategy = GenerationType.SEQUENCE)
    private Integer id;

    @Column
    private Integer value;

    @ManyToOne
    private EntitySuperClass entitySuperClass;


    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getValue() {
        return value;
    }

    public void setValue(Integer value) {
        this.value = value;
    }

    public EntitySuperClass getEntitySuperClass() {
        return entitySuperClass;
    }

    public void setEntitySuperClass(EntitySuperClass entitySuperClass) {
        this.entitySuperClass = entitySuperClass;
    }

}

Answer 1

在我的项目中是这样完成的:

@Entity
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "field", discriminatorType = DiscriminatorType.STRING)
@DiscriminatorValue("dummy")
public class EntitySuperClass {
    // here definitions go 
    // but don't define discriminator column here
}

@Entity
@DiscriminatorValue(value="sub1")
public class Sub1Class extends EntitySuperClass {
    // here definitions go
}

而且它有效。我认为您的问题是您在父类(super class)定义中不必要地定义了鉴别器字段。删除它，它将起作用。