On Wed, 2007-10-03 at 22:44 +0000, tzeskimo wrote:
> I'm trying to write a custom QuerySet, but I'm a bit confused about
> how to properly use the method extra(). From my understanding,
> extra() accepts both "select" and "where" arguments, both of which can
> contain bind variables. You then pass the appropriate bind variable
> values to the "param" argument.
>
> This method seems like it will fall apart if two QuerySets are chained
> together, both of which pass "select" and "where" arguments to extra.
> For example, wouldn't the following cause an issue:
>
> class FooQuerySet:
>
> def query1(self):
>
> self.extra(select = {'something': "item * %s"}, where = "item
> < %s", params = (3, 5))
>
> def query2(self):
>
> self.extra(select = {'something_else': "item / %s"}, where =
> "item > %s", params = (3, 5))
>
> model.custom_manager.all().query1().query2()
The "select" portion of extra() was never really intended to support
parameters. There are bigger problems than the one you've noticed here:
since "select" is a dictionary, it's ordering is indeterminate and so
when you have multiple items in the dictionary, there is no way to
reliably map the parameters to those items.
I've been toying with a couple of ideas in the context of the
queryset-refactor branch to possibly try and make this work (with a
little more effort on the side of the programmer), but it's never going
to be particularly neat and tidy.
For now, you can't do that. It's unsupported. You will need to write
custom SQL.
Regards,
Malcolm
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