Philip Hallstrom wrote:
> On Jan 12, 2010, at 9:46 AM, Steve Castaneda wrote:
>
>> I'm assuming my controller would look something like this for Widgets:
>> --
>>
>> I'm assuming that it has to go in some kind of condition. Am I
>> supposed
>> to run the owners find through some sort of block to validate for each
>> widget I've found in @widgets?
>
>
>
> @owners = Owner.all(:conditions => 'widget_id IS NULL')
No, you've got it backwards. Widget belongs_to :owner, so that won't
work.
The proper SQL query would be
SELECT * from owners o left join widgets w on (w.owner_id = o.id)
WHERE w.id is null
Deriving an AR find from that is left as an exercise. :)
>
> Would do it. Assuming that it's correct to say that if widget_id is
> null they have no widget -- this wouldn't catch instances where say an
> owner *had* widget, the widget was removed and the owners widget_id
> wasn't set back to null.
Nope.
>
> @owners = Owner.all.reject{|o| o.widget.nil? }
>
> Would also do it. This has the drawback that the DB is going to
> return *all* the owners and then filter them in ruby. Won't be as
> speedy as the first option.
Yup. It will work, but it's completely inappropriate to do this sort of
query in the app.
>
> You probably want to add an :order option to whichever one you use to
> get a consistent output.
>
> -philip
Best,
--
Marnen Laibow-Koser
http://www.marnen.org
[email protected]
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