Message Title

I agree that the test works with different join columns.
But the resulting table looks strange:
for each subclass i have to use it's own join column pointing to the same owning table:

CREATE TABLE `st_book` (
  `DTYPE` varchar(31) NOT NULL,
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `author` varchar(255) DEFAULT NULL,
  `name` varchar(255) DEFAULT NULL,
  `favoriteBookPersonId` bigint(20) DEFAULT NULL,
  `bookPersonId` bigint(20) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `UK_aswalvw2046e9u4ludbdiyayc` (`author`,`name`),
  KEY `FK_5eh9mtp3w94fp18u62gy34k2s` (`favoriteBookPersonId`),
  KEY `FK_6pl91a68ju1dcp1e881beghco` (`bookPersonId`),
  CONSTRAINT `FK_6pl91a68ju1dcp1e881beghco` FOREIGN KEY (`bookPersonId`) REFERENCES `st_person` (`id`),
  CONSTRAINT `FK_5eh9mtp3w94fp18u62gy34k2s` FOREIGN KEY (`favoriteBookPersonId`) REFERENCES `st_person` (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=latin1$$

I do not see why i should have an extra column in my table besides the DTYPE.
The test with the same column also works if i use the hibernate specific annotation @DiscriminatorOptions(force = true) in the super class:

@Entity
@Table(name = "ST_BOOK", uniqueConstraints = { @UniqueConstraint(columnNames = { "author", "name" }) })
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorOptions(force = true)  // prevent WrongClassException
public abstract class AbstractBook {
...

I'm still not convinced that these "solutions" are the way to go, especially not after playing with other JPA implementations.