On Fri, Apr 19, 2013 at 11:46 AM, Michael Bayer <mike...@zzzcomputing.com> wrote: > > On Apr 19, 2013, at 1:56 PM, Dan Lenski <dlen...@gmail.com> wrote: > >> The problem I'm having is... how can I figure out what are the appropriate >> type objects for this comparison if I *only* have access to the cursor >> object? > > > Basically I'd question that precondition. I'd look into how the system is > architected such that only a cursor is passed around, and try to substitute > it/augment it with some kind of contextual object; either an object that can > refer back to the DBAPI types, or even the DBAPI module itself. You can't > really assume that ".connection" is present, nor that the Connection class of > the DBAPI is in the same module space as where the type objects are defined. > I'd rework the system and refuse the temptation to guess.
I agree that my solution is not a good one... just a quick hack which seems to work for the modules that I've tried so far. However, it seems to me that the precondition is a reasonable one: the cursor object provides a DB-independent means of obtaining the data from a query, so why not the metadata as well? Actually, the DBAPI is pretty good in that regard, because it does establish the different type objects which a module must provide... but doesn't give a clear way to *find* those type objects from the cursor object. This makes it difficult to write truly DB-independent code to manipulate cursor objects. I *could* pass around a handle to the DB module along with the cursor itself, as you've suggested, but that seems redundant and error-prone to me. To my mind, this is a small gap in the DBAPI design: (1) DBAPI does specify a set of module-dependent type objects against which column type objects are to be compared (2) DBAPI does specify a cursor object which will produce column type objects after a query is executed (3) DBAPI *doesn't* provide any way to get from the cursor object to the module-defined type objects, at least not without passing around module-dependent object. Dan _______________________________________________ DB-SIG maillist - DB-SIG@python.org http://mail.python.org/mailman/listinfo/db-sig
