In theory it would be nice to enforce integrity constraints in only one place.
In practice, you'll probably have to compromise. Here are the reasons we had to
implement a hybrid solution.
1) Some integrity checks are much faster if implemented in the DBMS. For
instance, unique constraints would require an extra DB statement execution if
implemented in EJB instead of DBMS.
2) There is no standard exception (at least in practice) thrown by different
JDBC drivers and DBMSs for the same type of constraint. If you need to write
beans that support multiple drivers/DBMSs then you're going to end up with a lot
of messy code to in order to report an understandable error to the user.
3) Some DBMS cannot handle complex foreign key constraints. For instance, we
have some dependent objects (email & phone numbers) that can be attached to
various tables. This occurs because we chose to map various subclasses of people
and organizations to different tables. Stored procedures or triggers are
required for the logic needed to implement referential integrity for this case
in the DBMS. It much easier to implement this kind of constraint in the Entity
beans.
My two cents,
Victor Langelo
Gero Vermaas wrote:
> Hi,
>
> I had a discussion with a colleque of mine and we did not reach a agreement,
> maybe some experts on this mailing list can help us out....
>
> The question is: Should you use database level constraints to enforce the
> integrity of the database or is the integrity of the database the
> responsibility of the EJB?
>
> My collegues opinion is that it is the responsibility of the EJB to enforce
> the integrity of the data in the database. If you would implement this in
> constraints in the database then both the EJBs and the database would have
> to know about the integrity rules. Which is duplication of knowledge/logic,
> which is not a good thing.
>
> At first I agreed with him, but now I have second thoughts:
> - What if the database is used by other (non J2EE) applications? The
> integrity then must be maintained by the database, or should all
> applications be held responsible for the integrity? The latter would mean
> distributing the reponsibility over multiple applications, which is not a
> good thing? This would advocate to put the responsibility in the database
> and define the constraints there.
> - By putting the constraints in the database you enforce that their is one
> place where the data is consistent. Specific application could add
> additional constraints for that application into their logic, as long as it
> does not conflict with the data model.
>
> I'm anxious to hear your opinions on this....
>
> Regards,
>
> Gero Vermaas
>
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