Problem about mapping.

onur.aktas · **Joined:** Sun Oct 05, 2008 2:45 pm **Posts:** 8

Hi,
I have 3 Tables (I will give examples not exact tables but same structure and logic)

Code:

Cars :
   ID  ( Car ID)
   Name

Planes : 
   ID ( Plane ID)
   Name

Processes :
   ID ( Process ID )
   Type 
   VehicleID 

Sample Processes Table Data

Code:

ID     Type      VehicleID
---    -------      ------------
1          1               1        
2          1               2
3          2               1
3          2               2

When type is 1, This is Car and means that VehicleID maps to Cars Table,
When type is 2, This is Plane and means that VehicleID maps to Planes Table.
And So On 3, 4, 5, 6 .. for Additional tables.

How can i map something like that? I can not merge these tables, they all must be separated..

I used to handle this by writing native SQL with some functions, however with JPA i could not figure it out..

Thanks again
Regards.

gonzao_diaz · **Joined:** Mon Nov 26, 2007 2:29 pm **Posts:** 443

The problem with that kind of models, is that you cannot use foreign keys.

A partial solution for that, at least for Hibernate selects, would be to use 2 views and /or subselects on processes, and then perofroming Hibernate mappings on those views/subselects.

This will be only good for selection, though, you will still need a separate mapping to Processes as a whole for insertions.

Make sure to indicate in your mapping of the that the id generator for the views/subselects is "foreign", so that there are no conflicts with the id of Processes.

onur.aktas · **Joined:** Sun Oct 05, 2008 2:45 pm **Posts:** 8

Can you please give an example about that?