How to avoid polymorphism in superclass query when using JPA and Hibernate

Question

I use spring jpa+hibernate to connect to an Oracle DB with 2 tables: Customers and LegacyCustomers.

Customers extends LegacyCustomers by adding some additional columns.

@Entity
@Table(name="Customers")
public class Customers extends LegacyCustomers {
    @Column(name="NewId") private String newId;
    @Column(name="PhoneNumber") private String phoneNumber;
}

@Entity
@Table(name="LegacyCustomers")
@Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public class LegacyCustomers {
    @Column(name="OldId") private String oldId;
    @Column(name="Name") private String name;
    @Column(name="Address") private String address;
} 

However they are completely different tables. I am looking for a way to express the relationship in java but avoid the polymorphism that hibernate creates when querying the superclass table (LegacyCustomers). How can I tell hibernate to use only columns from the superclass when I query for LegacyCustomers?

Unfortunately the @Polymorphism annotation suggested here doesnt help.

Thanks for the help

Answer 1

To achieve your goal, you need to use the @MappedSuperclass annotation instead to a new BaseCustomers class that encapsulates the common properties:

@MappedSuperclass
public class BaseCustomers {
    @Column(name="OldId") private String oldId;
    @Column(name="Name") private String name;
    @Column(name="Address") private String address;
}

Afterward, the LegacyCustomers just extend the BaseCustomers and only adds the @Entity annotation since the BaseCustomers is not treated as an entity:

@Entity
@Table(name="LegacyCustomers")
public class LegacyCustomers extends BaseCustomers {

}

And the Customers entity does the same:

@Entity
@Table(name="Customers")
public class Customers extends BaseCustomers {
    @Column(name="NewId") private String newId;
    @Column(name="PhoneNumber") private String phoneNumber;
}

That's it.