[Zope] [OT] Example of Forcing Type coercion on a DCOracle2 column?
Wed, 19 Mar 2003 17:09:36 -0500
Thanks Matt. I've been able to get around the initial problem
I was having by using the XMLTYPE's getClobValue() to have
Oracle return a CLOB instead of the XMLTYPE, which was
causing DCOracle2 to Segfault.
However, no write()s to this CLOB ever get written back to
I've also discovered the Zope-DB mailing list, so I'll be using
that to post these types of problems from now on.
Matthew T. Kromer wrote:
> John Ziniti wrote:
>> Hello --
>> The DCOracle2 Documentation states that it is possible to force
>> type coercion on a result column to particular type, but does not
>> give an example of how to do this. Does anyone have any
>> suggestions? I am trying to force an XMLTYPE column into
>> a CLOB.
>> John Ziniti
> It doesn't go into detail because you really, really don't want to
> unless you know what you are doing.
> What the DCOracle2 type coercion does is assert to Oracle that the
> python object is whatever type you say it is.
> What this is most useful for is changing a string into something else
> -- but you have to be very careful that your input data is in fact
> properly formatted.
> For example, if I say
> import DCOracle2
> i = DCOracle2.TypeCoercion("foo", "SQLT_INT")
> I'm creating a coerced variable "i" that will claim to be an int. In
> fact, when Oracle goes to read it, it will read 0x666f6f00 (depending
> on the byte order). This may or may not be 1718578944 -- but it
> certainly isn't a very useful value. The coercion is applied AFTER
> the normal python type->oracle data type binding happens, ie it really
> just affects the bind declaration. If I coerce the number 1, I'm
> really referring to an address in memory pointing to a value
> containing 0x00000001 with a length of four bytes. When oracle is
> passed this pointer, its told what the data type is it points at. The
> TypeCoercion overrides what the declared type is, but doesn't
> *reformat* the data.
> Why would you want to do this? Well, maybe you want to handle the
> binary conversion of values yourself. The underlying C module dco2
> will let you get at the raw memory behind a result, so you could
> extend DCOracle2 to understand new types without writing additional C