使用每个层次结构的表时，将同一数据库列映射到Hibernate中子类的不同字段/属性

Question

I have a base (abstract) class A and two subclasses B and C which I want to persist them using table-per-hierarchy approach in Hibernate. Suppose B has 'width' and C has 'height' field which are of the same type. By default Hibernate creates two separate columns but fills only one column for each row. Now, what happens if I map both fields to the same column in DB, say 'length'?

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="type", discriminatorType=DiscriminatorType.INTEGER)
public abstract class A {
    @Id
    @GeneratedValue(strategy=GenerationType.IDENTITY)
    public Integer id;
}

@Entity
@DiscriminatorValue("1")
public class B extends A {
    @Column(name="length")
    public Integer width;
}

@Entity
@DiscriminatorValue("2")
public class C extends A {
    @Column(name="length")
    public Integer height;
}

I ran some basic tests and no error happened, but I didn't see anything like this in documentations -considering this practice prevents creation of lots of empty columns in a complex application and should be mentioned - and really don't have the expertise to declare this as a safe practice.

Has anyone done something like this? Are there any drawbacks to this approach? Also does the no-NOT-NULL-on-subclasses limitation holds in this scenario?

Answer 1

I have not encountered any problems after using this method for two years in production.

But notice that you cannot set different restrictions on fields because database sees them as one column.