[Zope] [OT] Example of Forcing Type coercion on a DCOracle2 column?
Matthew T. Kromer
Wed, 19 Mar 2003 16:50:13 -0500
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
For example, if I say
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 code.
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