[DB-SIG] Other extensions

[M.-A. Lemburg]

On 2007-05-15 21:00, Robert Brewer wrote:
> M.-A. Lemburg wrote:
>> On 2007-05-15 19:58, Art Protin wrote:
>>> No, this can not be done in a standard way above the DB-API
>>> level. There is nothing in the DB-API specification that can
>>> be used in a DBMS independent manner, that would be assured
>>> of producing the answers.  One would need to presume that all
>>> DBMSs have SQL access to the systems tables and ours for 
>>> one does not.
>> This depends on the database backend. Most of them provide
>> system tables with the needed information in one form or
>> another.
>>
>> Others don't and require using special interfaces (at C level).
>>
>> It's difficult to standardize. ODBC has gotten this pretty well
>> sorted out, IMHO, but emulating it in the DB API would be
>> quite difficult for the module authors.
> 
> It's not so much that making a standard interface is hard (SQLAlchemy,
> for example, and my Dejavu/Geniusql do this quite well). 

Well, it's finding the right attributes / selectors for the meta
data that's hard.

After all, the meta data should be as detailed
as possible, but not to a point where the majority of backends
wouldn't be able to support the interface or where writing the
interface for the meta data would require too much work (for
little value).

> It's that such
> interfaces are then called "Object-Relational Mappers" [1] and are
> pretty universally shunned as an arena for standardization.

I think we'd just need to standardize this at the DB-API level
if there are a significant number of database backends that
don't allow querying this meta data via cursor.execute().

Looking at your provider implementations:

http://projects.amor.org/geniusql/browser/trunk/geniusql/providers

it appears as if most databases do support this kind of
introspection. While for some you are using ADO (which essentially
uses the same meta data catalog API as ODBC), I think those
can also be covered using direct SELECT queries into the system
tables.

-- 
Marc-Andre Lemburg
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