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

[Amaury F. d'A. <ama...@gm...>]

Hello Anthony,

Anthony Tuininga 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?

Some wild thoughts, without any consideration of the diffulty to implement:

cx_Oracle types should be subclassable: the Cursor class and the Variable types.
When subclassing, users should be able to provide:

- OracleCursor.variableFactory(self, oracleType, <dataLength_and
others?>): the base implementation ends up by calling the current C
function "Variable_New" and returns its value.
Of course, when subclassing, users will want to substitute their own
udt_Variable class.

- OracleCursor.createRow(self): the base implementation is "Cursor_CreateTuple".
As an example of subclassing, I could copy it into a subclass of
tuple, with a custom __getattribute__ handling the column names...

- xxxVariable.getvalue and setvalue. Here can take place the
conversions to/from Zope datatypes.


Now, for the implementation:
The setValueProc and getValueProc members move from udt_VariableType
to udt_Variable.
Variable_New then checks for derived methods: if so, it replaces
setValueProc and getValueProc with appropriate wrappers like:
PyObject *derivedGetValue(udt_Variable *var, unsigned pos)
{
    return PyObject_CallMethod(var, "getvalue", "i", pos);
}
The advantage of this method is that advanced users can write their
own C code, derive DateTimeVar in C, and directly access the OCIDate*
buffer, with no performance penalty.

Thank you for having read so far.
Now my brain is too hot, I'd better go to bed...

-- 
Amaury Forgeot d'Arc