SINGLE_TABLE inheritance strategy using enums as discriminator value

Question

Is it possible to use an enum as a discriminator value when using SINGLE_TABLE inheritance strategy?

Answer 1

No, unfortunately you can't.

If you try to use an enum as discriminator value, you'll get a Type Mismatch exception ("cannot convert from MyEnum to String"), as the only discriminator types allowed are String, Char and Integer. Next, I tried using an enum's name and ordinal combined with DiscriminatorType.STRING and DiscriminatorType.INTEGER, respectively. But this didn't work either, as the @DiscriminatorValue annotation (as any other) requires a constant expression:

This doesn't work:

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="FREQUENCY",
    discriminatorType=DiscriminatorType.STRING
)    
public abstract class Event  {}

@Entity
@DiscriminatorValue(value=Frequency.WEEKLY.name())
public class WeeklyEvent extends Event {
    // Exception: The value for annotation attribute DiscriminatorValue.value must be a constant expression
}

Doesn't work either:

@Entity
@Inheritance(strategy=InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name="FREQUENCY",
    discriminatorType=DiscriminatorType.INTEGER
) 
public abstract class Event  {}

@Entity
@DiscriminatorValue(value=Frequency.WEEKLY.ordinal())
public class WeeklyEvent extends Event {
    // Exception: The value for annotation attribute DiscriminatorValue.value must be a constant expression
}