PL/SQL COMWRAP.SQL COM Automation in Windows

Question

Hello All,
Mike here. I'm not sure which forum this should go in so I put it here.
I'm writing a pl/sql procedure that calls ordcom (create by comwrap.sql) which uses orawpcom11.dll to work with com automation objects on windows. It appears that there is a limit on the amount of data that can be passed back to Oracle (approx. 34kb stored as a file). My best guess is that comwrap.sql doesn't provide for returned text steams that are larger than that provided by varchar2 in pl/sql. I tried adding to the comwrap.sql to have clob as a return type but that does not work.
I am attempting to get back XML from a Windows component (SDK to Quickbooks) that I can then store in an XMLType table. This works when all of the returned XML (from the SDK com object) stays under 34kb (stored as a file). If I remember correctly, 33950 characters are returned at the maximum. Of course, when the XML should be longer, I can't store it because it is not correctly formed XML (incomplete).
Does anyone know what is occuring and a way to get around this? Any help is appreciated.
Thanks,
Mike

Answer 1

The actual size is 32767 bytes Mike. And I'm not sure what happened to the last byte to make it 32768 and exactly 32KB. ;-)
You cannot change a varchar2 data type for a clob data type. These two types are quite different when it comes to memory allocation and management of variables of that type. These methods are incompatible. Essentially a clob variable is a "locator variable" (aka lob locator). Just another word for a pointer.
Declaring a clob variable is simply defining a pointer variable that, as yet, points to nothing. The clob needs to be created, memory allocated, and the point/locator must be set to this chunk of clob memory allocated.
Declaring a varchar2 variable results in the compiler doing the actual work at compilation time - reserving space for that variable and setting that variable's address to this preallocated space.
In terms of client-server, this a tad more complex. The data sits in the client. The data must be passed to the server. So there is a client variable. There is a server variable. And the content of one needs to be copied/pushed/transferred somehow from client variable to server variable.
Windows supports a set of data types. Oracle supports a different set. Why? Despite Oracle on Windows, Oracle also runs on something like a 100 other operating systems too. There are endian issues. CPUs dealing differently with reals and floats and integers. Oracle has thus its own abstraction layer and implement is own consistent set of data types - across all platforms.
So when pushing data from a client variable (like a COM object var) into a server variable (like a CLOB), it is not as simple as "copy-and-paste".
PL/SQL "understand" basic Windows data types like zero terminated strings - which it can accept into varchar2 variables. But as PL/SQL has a 32KB (less one byte) varchar2 limit, it cannot accept a huge Windows string (or data stream). And getting that to work via a clob, very likeky requires changes in the interface between client and server that does this transfer of data.
It requires more than just changing the server variable's data type from varchar2 into a clob, unfortunately. You will need to read up on Oracle's EXTPROC interface (I expect this is what is being used to interface with COM objects?) to see how to deal with LOB data types in this respect.