[DB-SIG] (Database Abstraction Layer) Wrapping DBAPI Exceptions

[Jon Franz_antispam]

As for PDO, it defines its own exception classes for the different types of
exceptions (connect error, etc),
and places information about the underlying db module specific exception
into the string description
of the exception.  Thus, users of PDO get one set of exceptions to trap for,
but still get all the information
they need to track down the cause.

~Jon Franz
NeuroKode Labs, LLC

----- Original Message ----- 
From: "Kevin Jacobs" <jacobs at penguin.theopalgroup.com>
To: "Peter L. Buschman" <plblists at iotk.com>
Cc: <db-sig at python.org>
Sent: Friday, September 26, 2003 7:31 AM
Subject: Re: [DB-SIG] (Database Abstraction Layer) Wrapping DBAPI Exceptions


> On Fri, 26 Sep 2003, Peter L. Buschman wrote:
> > The next thing I want to do is wrap the DPABI exceptions of the
underlying
> > driver and raise my own equivalents ( which will handle
> > exception arguments consistently... ) whenever they occur.  Here is the
> > strategy that comes to mind, but I am wondering how the rest of you
might
> > handle a case like this?
>
> My DB-API abstraction layer virtualizes exceptions by patching the base
> classes of the driver exception classes:
>
> abstract.py:
>
>   class Warning                  (StandardError)       : pass
>   class Error                    (StandardError)       : pass
>   class   InterfaceError           (Error)             : pass
>   class   DatabaseError            (Error)             : pass
>   class     DataError                (DatabaseError)   : pass
>   class     OperationalError         (DatabaseError)   : pass
>   class     IntegrityError           (DatabaseError)   : pass
>   class     InternalError            (DatabaseError)   : pass
>   class     ProgrammingError         (DatabaseError)   : pass
>   class     NotSupportedError        (DatabaseError)   : pass
>
>   dbapi_exceptions = [ 'Warning',
>                        'Error',
>                        'InterfaceError',
>                        'DatabaseError',
>                        'DataError',
>                        'OperationalError',
>                        'IntegrityError',
>                        'InternalError',
>                        'ProgrammingError',
>                        'NotSupportedError' ]
>
>   def __import_exceptions(module):
>     for e in dbapi_exceptions:
>       sub_exception    = getattr(module, e)
>       abstract_exception = globals()[e]
>       sub_exception.__bases__ += (abstract_exception,)
>
> Whenever I import a native DB-API driver, I call __import_exceptions,
e.g.:
>
>   import psycopg, MySQLdb, Sybase, PoPy, pgdb, MSSQL # ...
>   from   pyPgSQL import PgSQL
>
>   __import_exceptions(psycopg)
>   __import_exceptions(MySQLdb)
>   __import_exceptions(Sybase)
>   __import_exceptions(PoPy)
>   __import_exceptions(pgdb)
>   __import_exceptions(MSSQL)
>   __import_exceptions(PgSQL)
>
> Now I can catch any DB-API exception from the above modules without
knowing
> which one generated it.
>
>   def query(dbcon, sql):
>     cursor = dbcon.cursor()
>     cursor.execute(sql)
>     return cursor.fetchall()
>
>   def get_accounts(dbcon):
>     try:
>       return query(dbcon, 'SELECT ACCOUNTID FROM ACCOUNTS;')
>     except abstract.ProgrammingError:
>       # Do not trap errors due to bad SQL
>       raise
>     except abstract.DatabaseError:
>       # All other database related errors return empty results
>       return []
>
> Clearly, this example is a little contrived, but it gets the point across.
> The above routines do not need to know which underlying driver they are
> connected to to be able to catch exceptions.  Of course, there are a
> thousand _other_ things that are not abstracted in this example.
>
> Feel free to reuse the above idea.  Just mention me in the credits
> somewhere.  ;)
>
> -Kevin
>
>
> -- 
> --
> Kevin Jacobs
> The OPAL Group - Enterprise Systems Architect
> Voice: (440) 871-6725 x 19         E-mail: jacobs at theopalgroup.com
> Fax:   (440) 871-6722              WWW:    http://www.theopalgroup.com/
>
>
>
>