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Re: redesign exception

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On Sun, 26 Oct 2014 12:46:59 -0700, boxzou wrote:

> Here is a JPA exception I once tried to recover from (catch) ('a ->b'
> means b is a cause of a as in exception chaining):
>    PersistenceException -> DatabaseException -> BatchUpdateException ->
>    SQLIntegrityConstraintViolationException
> 
> And in the ultimate cause 'SQLIntegrityConstraintViolationException',
> there is a code 'ORA-00001' which mean unique constraint violated.
> 
> So I have to drill down all the way to find the ultimate cause, even on
> that one if I had to make sure, I would have called getCode() to see if
> it is 'ORA-00001'.
>
Yes, you do have to deal with all the exceptions in that list - and its 
nothing to do with Java specifically.

You are seeing this exception list because this is the behaviour of every 
RDBMS I've used: when an RDBMS throws an exception, that is merely the 
head of a list of related exceptions. To properly report what went wrong 
you have to work down the list, reporting the exception name and error 
message contained in each SQL exception in the list. That is required by 
the way that almost every RDBMS works.

Since an ODBC driver is a machine independent RDBMS interface, it follows 
that it also reports SQL exceptions by returning a reference to a list of 
exceptions. And, since a JDBC driver class follows the ODBC structure 
very closely and in many cases is implemented as an ODBC wrapper, it does 
the same. 

> An if I switch from Oracle DB to Derby DB, the chain of exceptions would
> be:
>   PersistenceException -> DatabaseException -> BatchUpdateException ->
>   SQLIntegrityConstraintViolationException -> EmbedSQLException ->
>   StandardException
> 
Of course: Oracle, Derby (and MySQL, MariaDB, PostgreSQL, SQLserver, 
Sybase, DB2, HSQL) are independently developed proprietary RDBMS (only 
PostgreSQL, HSQL and MariaDB are open source; MySql used to be), so their 
implementations are, of course different and so are the exceptions they 
throw in similar circumstances.

> Why do we have this kind of chaining?  because Java has checked
> exceptions.
>
Bollocks. You see it when using with JDBC or Reflection as RDBMS 
interfaces because this is what any RDBMS needs to do if it is to return 
an accurate description of what caused an SQL exception.

The *only* place you'll see such a chain in pure Java is 
when a higher level class catches an exception thrown by a method of a 
lower level class it called and, instead of dealing with the exception 
and throwing a more meaningful exception, chooses to build a chain by 
throwing an Exception containing its explanation plus a link to the 
Exception that it caught. I can't offhand think of many Java standard 
library classes that do this, but you *should* look for and follow these 
chains wherever they might be found if you use 3rd party class libraries. 
Yes, they should document their uses of such Exception chains, but they 
may have forgotten to do so. All RDBMS implement such chains and 
*document* the fact that they do so it should not come as a surprise.

   
> But even if we do away with checked exceptions, the
> exception type alone still is not sufficient to handle the exception. 
>
Disagree. 

Name or code, its utterly irrelevant which you get handed provided its 
unique. In C you get a (hopefully unique) exit code and are left to 
decide whether you want to handle it of not. In Java, you *must* catch a 
checked Exception but its up to you whether you're a lazy wazzock and 
deal with all Exceptions in a single portmanteau catch() clause or 
whether you are more careful and differentiate their handling with a set 
of catch() clauses.

> We still need to get a code to know exactly what happened.
>
Yeah. Its called the Exception name.

> with a code, e.g. unique constraint violated, but which unique
> constraint?  The constraint name is buried in the message, which is
> unstructured data.  I want structured data.
>
Sorry, but that's not what any RDBMS does. Live with it: its probably[1] 
written into the current SQL specification and is not going to change.
 
[1] 'probably', because the SQL standard is a paid-for document and I 
don't have access to a copy.


-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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Thread

redesign exception boxzou@gmail.com - 2014-10-25 19:16 -0700
  Re: redesign exception Joerg Meier <joergmmeier@arcor.de> - 2014-10-26 08:09 +0100
    Re: redesign exception rossum <rossum48@coldmail.com> - 2014-10-26 09:15 +0000
      Re: redesign exception Joerg Meier <joergmmeier@arcor.de> - 2014-10-26 10:36 +0100
      Re: redesign exception Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-10-26 09:23 -0400
        Re: redesign exception boxzou@gmail.com - 2014-10-26 12:56 -0700
          Re: redesign exception Eric Sosman <esosman@comcast-dot-net.invalid> - 2014-10-26 18:10 -0400
            Re: redesign exception boxzou@gmail.com - 2014-10-26 17:39 -0700
      Re: redesign exception boxzou@gmail.com - 2014-10-26 12:06 -0700
        Re: redesign exception Joerg Meier <joergmmeier@arcor.de> - 2014-10-26 20:41 +0100
    Re: redesign exception boxzou@gmail.com - 2014-10-26 12:46 -0700
      Re: redesign exception boxzou@gmail.com - 2014-10-26 13:12 -0700
      Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-26 16:50 -0500
        Re: redesign exception boxzou@gmail.com - 2014-10-26 17:21 -0700
      Re: redesign exception Martin Gregorie <martin@address-in-sig.invalid> - 2014-10-27 01:05 +0000
        Re: redesign exception boxzou@gmail.com - 2014-10-26 19:38 -0700
          Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-27 00:13 -0500
            Re: redesign exception boxzou@gmail.com - 2014-10-27 04:59 -0700
            Re: redesign exception Marketa Jadalova <m-jadalova3@gmail.com> - 2014-10-27 16:55 +0000
              Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-27 12:46 -0500
                Re: redesign exception boxzou@gmail.com - 2014-10-27 15:48 -0700
                Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-27 22:16 -0500
                Re: redesign exception Robert Klemme <shortcutter@googlemail.com> - 2014-10-27 23:54 +0100
                Re: redesign exception boxzou@gmail.com - 2014-10-27 17:20 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-28 07:12 -0700
                Re: redesign exception Robert Klemme <shortcutter@googlemail.com> - 2014-10-29 08:34 +0100
                Re: redesign exception Martin Gregorie <martin@address-in-sig.invalid> - 2014-10-29 11:17 +0000
                Re: redesign exception Silvio <silvio@internet.com> - 2014-10-29 15:33 +0100
                Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-29 11:35 -0500
                Re: redesign exception boxzou@gmail.com - 2014-10-29 17:51 -0700
                Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-29 20:45 -0500
                Re: redesign exception boxzou@gmail.com - 2014-10-30 04:12 -0700
                Re: redesign exception Silvio <silvio@internet.com> - 2014-10-30 12:38 +0100
                Re: redesign exception boxzou@gmail.com - 2014-10-30 06:23 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-29 17:01 -0700
                Re: redesign exception Marketa Jadalova <m-jadalova3@gmail.com> - 2014-10-29 16:55 +0000
                Re: redesign exception Martin Gregorie <martin@address-in-sig.invalid> - 2014-10-29 17:29 +0000
                Re: redesign exception Robert Klemme <shortcutter@googlemail.com> - 2014-10-29 18:59 +0100
                Re: redesign exception Martin Gregorie <martin@address-in-sig.invalid> - 2014-10-29 22:05 +0000
                Re: redesign exception boxzou@gmail.com - 2014-10-29 18:04 -0700
                Re: redesign exception Leif Roar Moldskred <leifm@huldreskog.localdomain> - 2014-10-29 20:56 -0500
                Re: redesign exception boxzou@gmail.com - 2014-10-30 04:19 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-30 04:27 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-30 04:35 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-29 18:01 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-29 17:00 -0700
                Re: redesign exception boxzou@gmail.com - 2014-10-29 16:56 -0700
    Re: redesign exception boxzou@gmail.com - 2014-10-26 12:52 -0700
  Re: redesign exception Silvio <silvio@internet.com> - 2014-10-27 09:03 +0100
    Re: redesign exception boxzou@gmail.com - 2014-10-27 05:06 -0700
      Re: redesign exception Silvio <silvio@internet.com> - 2014-10-27 13:32 +0100
        Re: redesign exception boxzou@gmail.com - 2014-10-27 07:01 -0700

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