在 joined inheritance 策略中查询基础实体怎么可能也获取子实体？

Question

I have an abstract base class:

@Inheritance(strategy = InheritanceType.JOINED)
@Getter
@Setter
@Entity
@ToString
public abstract class BillingDetails {
 @javax.persistence.Id
 @GeneratedValue(strategy = GenerationType.SEQUENCE,
        generator = "pk_for_inheritance")
Long Id;
@NotNull
private String owner;
}

and one subclass extending base class

@Entity
@Getter
@Setter
@ToString(callSuper = true)
public class CreditCard extends BillingDetails{

 @Basic(optional = false)
 private String cardNumber;
 @Basic(optional = false)
 private LocalDate expDate;
 @Basic(optional = false)
 private String cardKey;
 } 

when I query against base Entity BillingDetails and print results like so:

 List<BillingDetails> details=billingDetailsRepository.findAll();
 details.forEach(System.out::println);

I get the following output:

CreditCard(super=BillingDetails(Id=1, owner=Mehmet Dogan), cardNumber=6145 1233 4577 2360, expDate=2022-05-03, cardKey=673)

My question is: Although I understand in joined strategy hibernates joins related base and sub tables,How is it possible that I can print properties of subclass CreditCard when my result list is of type BillingDetails and only Id and Owner properties are declared in my base class?

Answer 1

What I have missed here was I think polymorphism. When I tried to get Class of results like

  List<BillingDetails> details=billingDetailsRepository.findAll();
  details.forEach(x-> System.out.println(x.getClass()));

I got the following output:

class com.rumlor.domainmodelmapping.models.inheritancemodels.CreditCard

so somehow I missed somewhere even if results are cast to List Of BillingDetails,Hibernate polymorphed every sub instance to base entity for me. additional check:

  CreditCard card= (CreditCard) details.get(0);
  System.out.println(card);

result:

CreditCard(super=BillingDetails(Id=1, owner=Mehmet Dogan), cardNumber=6145 1233 4577 2360, expDate=2022-05-03, cardKey=673)