[DB-SIG] autocommit support in pep-249

Vernon Cole vernondcole at gmail.com
Tue Sep 13 04:15:07 CEST 2011


This sounds like yet another item which should go into the dbapi 3.0
spec... as soon as someone has the courage to start one.
--
Vernon

On Mon, Sep 12, 2011 at 4:20 PM, Chris Clark <Chris.Clark at ingres.com> wrote:
> Hi All,
>
> I was discussing with someone today autocommit support and found an area of
> pep-249 where I think we could improve the wording (and the spec):
>
> http://www.python.org/dev/peps/pep-0249/
>
> .....
>
>       .commit()
>                    Commit any pending transaction to the database. Note that
>           if the database supports an auto-commit feature, this must
>           be initially off. An interface method may be provided to
>           turn it back on.
>
> .....
>
> It is the last sentence that I'm looking at:
>
>> An interface method may be provided to turn it back on.
>
> Comments:
>
>   * The "may" clearly marks this as an optional interface (and I'm
>     happy about that).
>   * It would be helpful to make clear what the interface method would
>     be so module authors can implement this consistently
>   * if autocommit can be turned on in a connection, there should have
>     a way to turn it off again
>
>
> Here are some examples of the "interface method" implemented out in the wild
> today
>
>   * It looks like mxodbc handles this as a setconnectoption() method
>     on the connection.
>     http://www.egenix.com/products/python/mxODBCConnect/doc/mxodbc/
>   * a number of other ODBC based drivers offer an option in the
>     connect() constructor (only)
>   * The mysql module <http://mysql-python.sourceforge.net/> implies it
>     has an method on the connection object for this conn.autocommit(),
>     but this does not appear to be available in the pep-249 compatible
>     API <http://mysql-python.sourceforge.net/MySQLdb-1.2.2/>!
>
>
> Obviously there is plenty of scope for different implementations. I think
> there is value in documenting a recommendation on what this interface should
> look like.
>
> I like the API approach mxodbc has taken (it matches ODBC very well) but it
> doesn't feel Pythonic :-(
>
> To get the ball rolling, here is an initial suggestion:
>
>   * needs to take a boolean flag as a parameter to enable and also disable
>   * needs to return the auto commit state so it can be queried
>
> pep changes, marked between ** and **:
>
> Connection Objects
>
>   Connection Objects should respond to the following methods:
> ......
>
>       .commit()
>                    Commit any pending transaction to the database. Note that
>           if the database supports an auto-commit feature, this must
>           be initially off. **See the option autocommit() method to change
>           autocommit behavior.**
>                      Database modules that do not support transactions
> should
>           implement this method with void functionality.
>
> .....
> **
>   Connection Objects may optional implement and respond to the following
> methods:
>
>   autocommit(on=None)
>      returns True when autocommit is on, and False when autocommit is off.
>      If the keyword parameter "on" is set to True, the connection will
> commit any open transactions (as if connection.commit() was issued) and all
> subsequent transactions will auto commit, the method returns True if
> successfully in autocommit mode.
>      If the keyword parameter "on" is set to False, the connection will
> commit any open transactions (as if connection.commit() was issued) and all
> subsequent transactions will no longer auto commit, the method returns False
> if successfully out of autocommit mode..
> **
>
> The reason for the immediate commit is to try and avoid DBMS specific
> behaviors (read error conditions) with different vendors when an auto commit
> is requested with open transactions.
>
> Comments?
>
>
> Chris
>
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