Find where association model count=0?

Rails
1

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?

Thanks!

2

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(foos.id) as
foos_count”,:joins=>“LEFT JOIN foos ON widgets.id =
foos.widget_id”,:group=>“widgets.id”,:having=>“foos_count=0”)

Yanni M. wrote:

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?

Thanks!

3

On Jul 6, 2:35 pm, Yanni M. [email protected] wrote:

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(foos.id) as
foos_count”,:joins=>“LEFT JOIN foos ON widgets.id =
foos.widget_id”,:group=>“widgets.id”,:having=>“foos_count=0”)

I think that

Widget.find(:all,:select=>“widgets.*”,:joins=>"LEFT OUTER JOIN foos ON
widgets.id =foos.widget_id ",
:conditions => “foos.id 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.

Fred