I have a legacy database, on which I have to develop an application. In one table there are two primary keys (two separate keys, not a composite key consisting of two columns!):
1. an uuid (surrogate key), which I can generate using Hibenate's uuid-algorithm and
2. an application specific id (customer number), which I have to generate using an existing sequence from the database.

The first I can generate using

<id name="id" type="string" unsaved-value="null">
<column name="UUID" sql-type="char(32)" not-null="true" />
<generator class="uuid.hex" />
</id>

the second I can generate using

<id name="custno" type="string" unsaved-value="null">
<column name="custno" sql-type="char(28)" not-null="true" />
<generator class="sequence">
<param name="sequence">CUSTNO</param>
</generator>
</id>

but not both at the same time.

Since I cannot have two <id>-elements in my mapping file I am looking for another possibility to map this table (without modifying it or creating new tables, as this is a legacy DB).

Any ideas?

Hibernate version: 3.0

- You can always keep one as the PK and turn the other into a unique-constrained column. The downside is that the generation of the second key is delegated to your class.

- You can write a custom type and a custom generator for that type. It's more work but generation will be handled by Hibernate.

- Finally, if you have two columns that are unique (meaning they are candidate keys) the tuple is also unique. You can treat them as a composite-key, but they will no longer be generated by Hibernate.

I would chose the first approach, defining a PK based on a sequence and implementing the generation of the UUID key within my class. The mapping would be something like:



I'm fairly new to Hibernate, so please take my advice with a grain of salt.

That is what I am doing right now. I just wondered if I could let Hibernate generate both ids.

You can write a user-type that encapsulates both the customer number and the UUID. You would need to write a custom generator implementing IdentifierGenerator that returns that user-type.

Your schema makes zero sense. If you hae a UUID, it is by definition unique of its own accord. It is the primary key. You don't need another column.

AFAIK, there is no database that allows two true primary keys in one table, either. You have to choose one of them (though the other can still be constrained unique)

Well, as I wrote in the beginning, it is a legacy DB, so I cannot change the schema, whether it make sense or not.



This is true, and I did so. I just wondered whether I could use Hibernate to generate both ids, one as the primary key and one as a unique column. But there seems to be not possibility. By now I have found another solution, although I cannot use Hibernates abstraction from the underlying database anymore, which is the drawback of this solution.

Please do not rate well-intentioned replies as "unhelpful".

Both of the responders in this thread were trying to help you, and hence their posts were literally "helpful".

If you speak English as a second language, please learn what "unhelpful" means:

http://dictionary.reference.com/search?q=unhelpful

ie. it is not the negation of "solves my problem".


(I just edited a much stronger rebuke, to allow for the fact that you may not be a native English speaker.)

Sorry, but I wasn't aware of the correct meaning (yes, I am not a native speaker). Also, I have just now learned the real importance of the credit points. Is there a way to change ratings?