O-R Mapping of BC4J Inheritance

Question

We're trying to use BC4J to model our existing database schema and we're having trouble when it comes to inheritance.
Basically, the way we represent inheritence in our database is with multiple tables. For a given inheritance relationship, we have one table with all the attributes of the base class and one table with the "extra" attributes of the subclass. There is a 1 to 0/1 relatipnship between the base table and the sub table.
From what I've read, BC4J doesn't support this mapping out-of-the-box, correct? Instead, Oracle advocates replicating the base class attributes in each subclass table. We don't want to do that.
I've read several threads that suggest there is a way to override the framework to support the inheritance mapping I've described, but all of them are light on specifics (e.g. "override doDML to do...something"). Has anyone developed a solution to this problem that they're willing to share? I'm new to BC4J, but it seems like this comes up often enough that a standard solution has probably been developed...?
Thanks for your time!

Answer 1

We advocate and include built-in support for using the inheritance mapping strategy that gives simplest queriability over the hierarchy of types stored in a table: using a single table with a discriminator column. Simply mark one of your super-entity's attributes as the discriminator (with the declarative checkbox propert in the Entity editor) and then assign a default value to the discriminator attribute so the framework knows what discriminator value will represent the current type. For derived sub-entities, override the inherited discriminator attribute by re-adding it to the entity again -- using the admittedly oddly named (New From Table...) button -- and then override the default value of the discriminator attribute in the subentity to a distinct value that represents that entity type. Then, building polymorphic view objects that query over common attributes and return the property entity subtypes in each queried row is automatic.
We also support easily the mapping strategy that has each sub-entity in its own table.
One entity mapped to multiple tables requires either hiding that fact from BC4J by creating a database view over it, or requires overriding the doDML() method in your entity impl subclass.