Rails - Oct 2007 - Finding "has_many :through" items without any associated items

Hi guys,

I have a

class Foo
  has_many :foo_bars
  has_many :bars, :through => :foo_bars
end

What''s the simplest way to find all Foos that don''t have any
Bars?

I know I could go through some convoluted process like finding all Foo ids and
then finding all foo_ids from the foo_bars table and subtracting those, but it
seems like there should be a simple query to do this. Any thoughts?

Thanks in advance


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Foo.find :all, :include => foo_bars, :conditions => "foo_bars.id is  
NULL"
maybe (or write out the left outer join on foo_bars, either way is good)


Fred



On 2 Oct 2007, at 15:42, Gareth Adams wrote:
>
> Hi guys,
>
> I have a
>
> class Foo
>   has_many :foo_bars
>   has_many :bars, :through => :foo_bars
> end
>
> What''s the simplest way to find all Foos that don''t have
any Bars?
>
> I know I could go through some convoluted process like finding all  
> Foo ids and
> then finding all foo_ids from the foo_bars table and subtracting  
> those, but it
> seems like there should be a simple query to do this. Any thoughts?
>
> Thanks in advance
>
>
> >

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