I am currently trying to build a new Java application on top of an
already existing database which cannot be modified, because an old
application is working with it. The database contains a major
design problems:

Relations are implicit; this means we have quite many relations
between the tables, but these are not defined as FOREIGN KEY. So the
application must "know" what the relations are, it is not possible to
extract this info from the database schema itself.

I want to create an object-relational abstraction layer using hibernate which would implement the relation constraints and things like ON DELETE CASCADE and ON UPDATE CASCADE. Exactly like in your case, I cannot change the database schema to implement the constraints without crashing the legacy application.

What should I do?

Here's what I intend on doing:

- Copy my original database schema into a dummy database
- Modify the dummy database schema to implement the relationship constraints (foreign keys, - on delete, on update)
- Use middlegen on the dummy database schema
- Use the generated java classes on my original database schema

Is it how this should be done? Do you have any comments or suggestions? Do you know any references which could help with this kind of problem?

Thank you,

Best regards,


Simon

This question would have been best asked in the tools forum - in anycase I spotted it.

Middlegen can be used on a non-constrained database but you need to define the relationships using crossref tags for each table. Obviously, your other idea is another option. If you constrain the database it would be better if you could retain it. I suspect that you will have al sorts of data issues otherwise - even if both applications can run the old app will be an issue for the hibernate app as its not guaranting data is clean. Your probally know all of this and are stuck but this would really worry me if I was looking at this work.

Cood luck.