I have 2 classes, A and B:

public A
{
public List<B> list1;
public List<B> list2;
}

public B
{}


Is there a way to implement this through the hibernate mapping files such that:

1) There is only one class B (no empty subclasses solely for discriminator values)
2) There is only one table in the database

I can use the "where" clause in the mapping files, but I don't see anything to specify a discriminator value for a collection upon insert.

Thanks in advance.

You haven't provied enough detail on what the differences are between list1 and list2.

Ryan-

There isn't any difference... except that they're different lists. They're the same collection structure, same type in the collection, just different instances.

For example:

public PetSanctuary
{
public List<String> catNames;
public List<String> dogNames;
}

except with a user-defined type instead of String.

Edit:

Example hbm file


However: The above does not work because the database does not see the lists as separate, since all they have is a foreign key... so when you repopulate the lists, both lists will have all items from both lists in them. This is easily solved by a discriminator, except that the only way to populate a discriminator value (that I've seen) is to use subclassing, which is not a good thing in this case.

Hi Sutherlands,
were you able to solve the problem? I'm having the same issue ...

Unfortunately not the way I wanted. If you're just looking for a solution try any one of these:

1) Create mapping tables in your database - clean and easy, my recommendation
2) Use subclassing with a where clause in your hbm and a discriminator value - make a list of subA and a list of subB instead of 2 lists of 'class'
3) Put the discriminator value in the POJO - Ugly, and forces a lot of ugly code - the POJO shouldn't know what list it's in
4) Create completely different POJOs - doubles maintainance.

What I ended up doing was to create a new class to that "holds" a list, and added getter/setter to my original class that converted from the original List's to two objects and vice-versa
class A{
List<T> a;
List<T> b;
getList_a_AsObj(){
//returns an instance of B<T> containing the list a
}

}
class B<T>{
List<T>a;
}

so now the table corresponding to A has two foreign-keys to a new table corresponding to B, and simple list mapping for the rest....

In my opinion, having two foreign keys to the same object, where one of them is null, is a bad way to solve the problem.

I think you got me wrong ... (sorry if the code piece wasn't explanatory)

class A contains two instances of B (b1,b2), each containing one of the lists(list1,list2),
the new getter/setter methods (for b1,b2) are responsible for converting between list1,list2 and b1,b2 (and do whatever checks required)

So as far as hibernate is concerned A contains two references to two different instances of B, while B contains one single list of a kind.