find where association model count=0 ?

I have a widget model that has_many foos. I want to find a list of
widgets that have no foos. Can I do this with a "find" method? Right
now I am selecting all widgets and iterating through them to look at
.count. I know there is a better way to do this, but I haven't been
able to figure it out with a single SQL query. Any ideas?


I figured it out right after I posted :wink: Always happens like that..
Here is the solution (or one of them)

@widgets = Widget.find(:all,:select=>"widgets.*,count( as
foos_count",:joins=>"LEFT JOIN foos ON =

I think that

Widget.find(:all,:select=>"widgets.*",:joins=>"LEFT OUTER JOIN foos ON =foos.widget_id ",
:conditions => " is NULL")

might be faster (since the database can infer from that that you want
widgets with no foos which is a bit less work than doing all the
counting and then filtering that.