[DB-SIG] autocommit support in pep-249

[Chris Clark]

M.-A. Lemburg wrote:
> Chris Clark 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
>> ...
>> Comments?
>>     
>
> mxODBC and mxODBC Connect will support a writable connection
> attribute connection.autocommit to turn the feature on/off.
> This works by assigning a boolean to the attribute. The
> attribute also allows for an easy way to check whether autocommit
> is active or not.
>
> They both already support doing this via the (non-standard) DB-API
> extension connection.setconnectoption() method.
>
> From an API perspective, using an attribute is the right
> and user-friendly approach. My only gripe with this is the fact,
> that querying or setting the attribute can cause exceptions,
> which you'd normally only expect from function/method calls.
>
> Other than that I'm +1 on adding the attribute as standard
> DB-API 2.0 extension.
>
>   

Thanks M.A..

It looks like we are heading towards a consensus on an exception being 
used (when mid transaction and autocommit on is requested). So we should 
document that, I'm inclined to be a little whishy-washy and have a short 
line along the lines of:

    If an attempt is made to enable autocommit mid transactions this is 
likely to cause a DBI exception, the exception raised may vary between 
drivers/backends but will be a sub-class of driver.Error.

I'd like to try and cover the case mentioned above, where "*querying* or 
setting the attribute can cause exceptions". Is this likely? If so we 
should document that with a one liner too.

I'd like to steal your wording for documentation, I've only changed the 
first few words:

---------
A connection may optionally support a writable connection
attribute connection.autocommit to turn the feature on/off.
This works by assigning a boolean to the attribute. The
attribute also allows for an easy way to check whether autocommit
is active or not.

If an attempt is made to enable autocommit mid transactions this is 
likely to cause a DBI exception, the exception raised may vary between 
drivers/backends but will be a sub-class of driver.Error. A driver may 
choose to implement autocommit manually (that is, manually issue commits 
at the end of each cursor operation), to raise an exception if mid 
transaction, or pass the autocommit request to the backend and raise an 
exception for errors that the backend raises.
---------


It may be that we have more discussion on the commit/rollback options 
but I'm not planning on raising those options again unless there is 
interest from other posters.

RE the conn.begin() that is a -1 from me, this seems like a separate 
item to autocommit and may deserve a new thread. This doesn't prevent 
implementers from adding a non-standard exception though if it will 
prove to be useful for some users.

Chris