Is there any facility for having multiple DiscriminatorColumns when implementing Single Table per Class Hierarchy Inheritance?? Consider the following table:

BILLABLE_OBJECT
{
ID VARCHAR,
BILLING_SCHEDULE_TYPE VARCHAR, // YEARLY or MONTHLY
IS_FINANCABLE VARCHAR, // YES or NO
PRICE REAL
}

What if the class then depended on both the BILLING_SCHEDULE_TYPE and the IS_FINANCABLE fields to make a class hierarchy like the following:

abstract class Billable
{
...
}

// if BILLING_SCHEDULE == MONHTLY
abstract class MonthlyBillable extends Billable
{
....
}

// if BILLING_SCHEDULE == MONTHLY and IS_FINANCABLE == YES
class FinancableMonthlyBillable extends MonthlyBillable
{
..
}

// if BILLING_SCHEDULE == MONTHLY and IS_FINANCABLE == NO
class NonFinancableMonthlyBillable extends MonthlyBillable
{
...
}

// if BILLING_SCHEDULE == YEARLY
class YearlyBillable extends Billable
{
...
}

// if BILLING_SCHEDULE == YEARLY and IS_FINANCABLE == YES
class FinancableYearlyBillable extends YearlyBillable
{
...
}


// if BILLING_SCHEDULE == YEARLY and IS_FINANCABLE == NO
class NonFinancableYearlyBillable extends YearlyBillable
{
...
}

This hierarchy can be represented in one table where the class of a row is determined by more than one field in the table. In my current database I currently have a situation similar to the above example. If only one DiscriminatorColumn can be specified for a class then I cannot support my class hierarchy in EJB3.0 annotation semantics, as the way it currenly works is by using several fields to determine the class of a row. Is there any way to support this in ejb 3.0, other than adding a new column to my table that is a concatenation of the other columns that are used for determining object class, and then using it as the DiscriminatorColumn??

I've noticed that there is a hibernate specific way to do this by using @DiscriminatorForumla, but this is hibernate extension and not a part of the EJB3.0 spec. Is there any way to achieve the above that conforms to the ejb3.0 spec??

not in an EJB3 compliant way

if necessary, I may try using the hibernate extension for doing this. However, I couldn't really tell how to use the @DiscriminatorForumla from the documentation I found at http://www.hibernate.org/hib_docs/annot ... ml#d0e1999

It only shows the following:

@Entity
@DiscriminatorForumla("case when forest_type is null then 0 else forest_type end")
public class Forest { ... }

Is there some more documentation available for this annotation and/or possibly even an example somewhere that shows how to use it?? Any information regarding this would be greatly appreciated.

there should be some examples of formula in a discriminator in the hibernate core reference documentation