[odb-users] Catch Exception Problem

[Tarik BENZ]

Thank you very much, now the exception is caught.

Best
  Tarik

> Date: Thu, 30 May 2013 12:03:52 -0400
> From: boris at codesynthesis.com
> To: tenchu.tarik at hotmail.fr
> CC: odb-users at codesynthesis.com
> Subject: Re: [odb-users] Catch Exception Problem
> 
> Hi Tarik,
> 
> Tarik BENZ <tenchu.tarik at hotmail.fr> writes:
> 
> > The problem is that this exception is not caught by my code.
> 
> All ODB exceptions derive from the odb::exception base, so if you
> catch that (as you do in your code), then you should be catching
> any ODB exception.
> 
> 
> > template<typename Type> bool CreateNewObject(Type * object)
> > {
> >     if(object != NULL)
> >     {
> >         transaction * transact = NULL;
> >         try
> >         {
> >             std::unique_ptr<odb::database> db (create_database());
> >             transact  = new transaction (db->begin());
> > 
> >             // Make object persistent.
> >             db->persist((*object));
> >             transact->commit();
> >         }
> >         catch (const odb::exception& e)
> >         {
> >             cerr << e.what () << endl;
> >             if(transact != NULL)
> >             {
> >                 transact->rollback();
> >             }
> >         }
> >     }
> >     return false;
> > }
> 
> What can happen here is that the call to rollback() inside your
> exception handler can throw. This is actually a good example of
> how not to do it. Don't allocate the transaction object with new --
> just allocate it on the stack. If it is destroyed before commit()
> has been called (e.g., because an exception is thrown before you
> got a chance to call commit()), then it will automatically roll
> the transaction back. Also after certain failures (e.g., a connection
> is lost) it is pointless to try to call rollback. ODB is smart
> enough to handle that while your home-made auto-rollback is not.
> 
> So, if I had to reimplement your code, it would look like this:
>   
> template<typename Type> bool CreateNewObject(Type * object)
> {
>   if(object != NULL)
>   {
>     try
>     {
>       std::unique_ptr<odb::database> db(create_database());
>       transaction t (db->begin());
> 
>       // Make object persistent.
>       db->persist(*object);
>       t.commit();
> 
>       return true;
>     }
>     catch (const odb::exception& e)
>     {
>       cerr << e.what () << endl;
>     }
>   }
>   return false;
> }
> 
> Just realized another problem in your code: the database instance
> will no longer exist in the exception handler where you try to
> rollback the transaction started on this database. And the exception
> that you are unable to catch is most likely access violations.
> 
> Boris