Rails, ActiveRecord, how to find foreign rows that are NOT there?

Posted by randombits on Stack Overflow See other posts from Stack Overflow or by randombits
Published on 2010-05-28T20:38:30Z Indexed on 2010/05/28 20:42 UTC
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The title is a bit difficult to put together for this question.

Say I have two models, Foo and Bar. Foo has many Bar's. Bar belongs to one Foo. How do I use Foo.find to find all of the Foos that currently have zero Bars? In SQL this would translate into something like:

SELECT * from foo where id NOT IN (select foo_id from bar);

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