Is it possible to fetch all child entities from a parent abstract entity?

Question

I'm trying to figure out if I can make a method that fetches or finds all the entries in a central database I have.

My entities are as follows:

Nomination(Abstract) -> Type1Nomination, Type2Nomination, Type3Nomination, so on.

Nomination has a table is mapped to the DB also, and has the common properties/columns of every type of nomination. The rest is self-explanatory.

The way I see it, I would have to cast the types of nominations to the base class? And this would be done in a Service class (because you cannot make a DAO of an abstract class), am I correct?

Answer 1

You can do this in JPA/Hibernate and JPA inheritance. It should be as simple as querying the Nomination entity.

Select n From Nomination n

should return a list of abstract nomination objects.

I've seen folks using a type column in conjunction with the in keyword to get certain subgroups in your case something like

Select n from nomination where n.type in :types 

where types was a collection of "Type1Nomination" "Type2Nomination" but because these are sibling queries it can lead to some nasty LEFT OUTER JOIN queries