Hibernate,单表继承和使用来自超类的字段作为鉴别器列

Question

我有以下类型的hibernate实体层次结构的类.我想要有两个具体的子类Sub1Class和Sub2Class.它们由在field中定义的鉴别器列()分隔MappedSuperClass.有一个抽象的实体类EntitySuperClass,由其他实体引用.其他实体不应该关心它们是否实际引用Sub1Class或Sub2Class.

这实际上可能吗？目前我收到此错误(因为列定义在Sub1Class和EntitySuperClass中继承两次):

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

如果我想补充@MappedSuperClass到EntitySuperClass,然后我得到断言错误的的Hiberante:如果一个类既是实体和映射超类它不喜欢.如果我@Entity从中移除EntitySuperClass,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,所以如果可能的话,不应该更改.

我的课程:

@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,它是这样完成的:

@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
}

它有效.我认为你的问题是你在超类定义中不必要地定义了鉴别器字段.删除它,它会工作.

Answer 2

为了使用鉴别器列作为普通属性,您应该将此属性设置为只读insertable = false, updatable = false.由于您无法更改MappedSuperClass,您需要使用@AttributeOverride:

@Entity 
@Table(name = "ACTOR") 
@Inheritance(strategy=InheritanceType.SINGLE_TABLE) 
@DiscriminatorColumn(name="field", discriminatorType=DiscriminatorType.STRING) 

@AttributeOverride(name = "field", 
    column = @Column(name="field", nullable=false, length=8, 
        insertable = false, updatable = false))

abstract public class EntitySuperClass extends MappedSuperClass { 
    ...
}