Re: [cx-oracle-users] Modifying fetched data python types for zope adaptor

[Andy H. <and...@gm...>]

Hi Anthony, thanks for the fast response.

I'd thought about doing something similar to your suggestion for subclassing
cx_Oracle.Cursor and converting the types on the fly, but like you said
there's a performance hit. I'll probably implement this anyway so old
versions of cx_Oracle can be used.

Your second suggestion is definitely something that'd be much appreciated by
me. Both the psycopg2 and MySQLdb modules implement something similar.
Here's a quick summary of what they do:

With MySQLdb you can define a dict, keyed on the modules database types
(much like cx_Oracle.NUMBER) with the values being callables which return
the desired objects type. The callable is passed a string representation of
the data returned, and it returns a python object of the desired type. The
conversion dict is passed as an argument to MySQLdb connect method. See:
http://sourceforge.net/docman/display_doc.php?docid=32071&group_id=22307#functions-and-attributesfor
more details (search for conv)

psycopg2 defines a bunch of methods in its extensions module which do pretty
much the same thing. You define a casting method by tieing a function to a
Postgresql type via the types OID using the method
psycopg2.extensions.new_type and then psycopyg2.extensions.regster_type. As
with MySQLdb a string representing the returned data is passed to the
conversion function, and the conversion function returns a python object.
More info at
http://initd.org/tracker/psycopg/browser/psycopg2/trunk/doc/extensions.rstand
search for "Type casting of SQL types into Python values".

Which really is pretty much the same as your settype(cx_Oracle.DATETIME,
<YourTypeOrMethod>). I guess the one thing they do in common is pass a
string to the conversion method, although it'd probably be as simple to pass
cx_Oracles native value for the given type, i.e. a datetime (or
cx_Oracle.Date) for cx_Oracle.DATETIME and so on. After all if I'm defining
the conversion methods then I should know what I'd be getting.

Thanks again in advance. Sorry for going on so long there.

Andy


On 11/9/06, Anthony Tuininga <ant...@gm...> wrote:
>
> There is no way of hooking into the returning of date objects. You'll
> have to hook the entire result set. You can do that quite easily by
> subclassing cx_Oracle.Cursor and overriding fetchone(), fetchmany()
> and fetchall() to transform any datetime.datetime entities into Zopes
> DateTime objects. Clearly there is a performance penalty in doing
> this. If you can suggest an alternative that would eliminate the
> performance penalty I'd be happy to entertain it. Perhaps something
> along the lines of settype(cx_Oracle.DATETIME, <YourTypeOrMethod>)
> which would then call <YourTypeOrMethod> with a particular set of
> parameters? Any thoughts on this?