Polymorphism question (please help)

guy · **Joined:** Fri Sep 15, 2006 6:07 am **Posts:** 5

Hi all,
I am using Hibernate 3.1 and I am facing the following problem, somehow I have the feeling that I am missing something and the solution is quite simple :-)

I have two classes, Device:

Code:

public class Device  implements Target
{
    public String ip;
    public String hostName;
    ....
}

and Company:

Code:

public class Company  implements Target
{
    public String name;
    public String version;
    ....
}

These classes are successfully mapped to DEVICE_T and COMPANY_T respectively.
In addition I have a class that associated with Target (i.e.Device or Company) as follow:

Code:

public class Task
{
    public Target target;
}

My Question is how can I map the Task class?

Thanks in advance,
Guy

scarface · **Joined:** Sun Jun 04, 2006 1:58 am **Posts:** 136

you need 2 coulmns in the table mapped to Task class

1. Descriminator coulmn which tell it what kind of target to get
2. foriegn key coulmn

and you need to map target many-to-one using the any mapping

check this out for more info
http://www.hibernate.org/hib_docs/v3/reference/en/html/mapping.html#mapping-types-anymapping

stolley · **Posted:** Mon Dec 11, 2006 12:31 am

Is there any way to map this reference using multiple database columns?

The discriminator column + "any" mapping means we would have to give up referential integrity on that column.

When we have a small number of possible subclasses of the interface, we'd like to map the association with two (or three) explicit foreign key relationships (only one of which would ever be set at any point in time for a given row).

At the moment (in terms of the example given by Guy) we are achieving this by explicitly mapping Company and Device properties on the Task class (which are not exposed to the business logic of the application), then we use a bunch of messy and potentially error-prone if/else code to set/get return a single Target instance depending on which type of explicit property has been/is being set.

If there's no mapping in Hibernate that could achieve this, would the dev team be willing to accept a patch that did this?