Hi,
I've recently read Malcolm's blog entry about __iter__ and __len__ in the
refactored QuerySets. Interesting!
In the refactored QuerySet, if you do e.g.
if models.Something.objects.all():
...
then QuerySet.__nonzero__ will execute the query and try to fetch the first
result.
I see one possible problem: I observe that mysql always slurps in the
whole result set from the database when you only issue a select
(cursor.query(...))
If you dig into MySQLdb, you see how it happens at cursor.py (of MySQLdb):
Cursor.execute() calls Cursor._query()
Cursor._query() calls Cursor._do_query()
Cursor._do_query() calls _do_get_result()
... which eventually fetches all (!) results from MySQL.
Mysql provides a CursorUseResultMixIn, but this has the restriction that
"You MUST retrieve the entire result set and
close() the cursor before additional queries can be peformed on
the connection."
... and that's not what we want, either.
Theoretically, it's probably possible to work around this, since the C API
has a function to free the result set. Another solution could be to let the
database backend decide whether it's better to use count() instead.
Michael
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