[Zope] mxODBC, ExtensionClass.Missing and Results puzzle???

[Jay, Dylan]

I've compiled up a mxODBC DA for use under windows so that multi-threaded
odbc drivers can be me used in a  multi-threaded way.

This works good so far except for one aspect. NULL values are being returned
as "None" objects. This seems reasonable but it is not how ZODBC returns
results. It will return a NULL as a "Missing" object (whatever that is?). I
can't find any documentation to find out what this object is or means. 
My biggest problem is that the UserDB product doesn't like None objects
being return for passwords. It seemed to handle the Missing objects fine.

To add to the mystery I noticed that the result object returned by an sql
method connected to first ZODBC and then ZmxODBC was of two different types.
ZmxODBC was returning a ZRDB.Results object. ZODBC was returning a
ZRDB.RDB.DatabaseResults object. The latter is apparently a "Class for
reading RDB files" but as this is the only documentation I can find I have
no idea how it differs from the ZRDB.Results class or rather why ZODBC
returns it and thus has NULL's replaced Missing objects.

Can anyone shed any light on any of this?

----
Dylan Jay                           mailto:djay@avaya.com
Avaya Communication                 Tel:   +61 2 9886-8961
Level 5, 15 Talavera Road           FAX:   +61 2 9352 9224
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