Re: Unique fields

From: Stefaan Huysentruyt (
Date: Tue Oct 05 2004 - 11:51:24 EDT

  • Next message: Gentry, Michael: "Is it OK to model multiple relationships to the same table?"

    On 5-okt-04, at 16:52, Cris Daniluk wrote:
    > Why not let the database do it and simply have the db adapters better
    > equipped to handle the unique constraint exception?

    > -----Original Message-----
    >> From: Gentry, Michael []
    >> My approach for the e-mail address would be to use
    >> validateForSave() to query the table (if the object hasn't
    >> been inserted yet -- look at
    >> PersistenceState.NEW) and handle it there. That way you don't
    >> have to sort out the exceptions and can give a nice error
    >> message to the user.

    Me too I have some doubts.

    The DBMS handles the persistence of your objects, and its own

    Even if you handle possible duplicates in your validateForSave(), I
    think you could still be forced to handle an (the unique contraint)
    exception triggered by the DBMS at commit time. Other aplications or
    threads could have just inserted or removed the eventually triggering
    row. This depends on tactics, and - case per case - the complexity of
    your application architecture and overall deployment. Maybe therefor
    depending, for contraint checks, on the ORM framework that is Cayenne
    is not such a good idea.

    What does sound interesting though, is a way to create wrapper
    Exceptions for common DBMS "runtime" exceptions like these. These
    could be a refinement of the CayenneRuntimeException. For example, the
    DataContext or the Query could then be configured to raise an exception
    if no rows are found for a Query.

    But then again, because each database product differs, making
    exceptions more semantic probably implicates work to be done at the
    adaptor level too. Or one could choose to have a look at the SQL92 ISO
    standard error codes and think what we could do using these. Etc...
    choices, choices...

    Just my 0.02

    I have some experience with EOF, and now looking at Cayenne. So i'm not
    really ready yet for in depth discussions. So I could be wrong,

    Stefaan Huysentruyt

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