Thursday, November 13, 2008

I was wrong

Tomorrow I will deliver (using the English language) my second presentation in an international Microsoft conference. My first time ever was in 2005 in Nice for the now defunct MEDC (Mobile and Embedded Developers Conference). I have been splitting my time in attending interesting presentations, preparing my own presentation and completing the OLE DB Client library code. It was while working some final details of the presentation that I had an epiphany: I was wrong about BLOB command parameters!

The fact that the OLE DB specification limits us to using just one parameter accessor handle to set all the parameters does not mean that we are unable to use storage objects. Why? When I discussed the limitation of the SQL Compact engine that prevents it to create more than one storage object at the same time, it actually applies to when the data flows from the provider to the consumer, like when you are reading data from a base table cursor or from a query cursor. It does not apply to when data flows from the consumer to the provider. In fact, we experienced no such limitation when inserting or updating data through a base table cursor. The consumer application can create as many storage object as it pleases to, and this is the exact same situation with command parameters: the consumer application can only write to them because SQL Compact does not support output parameters.

Right now this is still a theory that seems to make a lot of sense to me and I will focus now on proving it right. Meanwhile, I developed a new set of classes to manage column values in such a way that they would do double duty when used on a rowset and on command parameters. For the latter, these classes would work as intermediate data buffers that would be used as temporary storage for application-provided parameter data. When needed, the CCommand code would bind these to a real data buffer, recreating the accessor handle when needed. In fact, I have just tested the code and it works... But this can't be right. If I can bind the parameters before setting them (just like in the CRowset class) then I will have the best solution.

Back to the drawing board. (If you want to see the code as it is, please drop me a line.)

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