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
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