HOWTO create a polymorphic View Object .

Question

I 've a table say "people" wich contains a discriminator column (say sex) and some data depending on that attribute.
I'm able to create an entity people and the 2 extending entities Man and Woman and the related Vo.
Now I need to create a complete VO wich includes attributes from People, Man and Woman in order to create a maintenance program for that table (I'd like to avoid a double or triple maintenance program) wich exposes all attributes switching off the attributes wich are not related to the row the user is operating on.
I mean the Vo should expose People+Man attributes if it's a man and People+Woman attributes if it's a Woman.
Is it possible ? How ?
Tks
Tullio

Answer 1

There are two ways that could possible solve your needs:
1. Create two or n 'leaf' VOs per subtype. And use the allEmpVO to find the row you are interested in and then use it's key to find the row in an appropriate VO subtype to fetch all the subtype VO properties that are not part of the base.
2. Use a custom attribute mapping by overriding getAttribute(String/int) methods and map extra subtype specific attributes to predefined generic names and based on the discriminator, in the generic attribute getter, unmap it back to the corresponding subtype attribute value. Something like say create ATTR1, ATTR2, ATTR3 etc on the base subtype. Override the getters for these attributes to fetch the subtype entity and fetch a subtype attribute value. Note that you may also have to implement mapping of subtype attribute names to ATTR1, ATTR2 etc so that on the caller side you could call getAttribute(subTypeAttrName) and that gets mapped to say ATTR1 which ends up calling subtype's getAttr1 method and return getEntity(subTypeEntityIndex).getSubTypeAttr1()