How to filter by association count?

Question

Let's say I have models that look like this:

class Foo < ActiveRecord::Base
    has_many :bars, :through => :cakes
    has_many :cakes
end

class Bar < ActiveRecord::Base
    has_many :foos, :through => :cakes
    has_many :cakes
end

class Cake < ActiveRecord::Base
    belongs_to :foo
    belongs_to :bar
end

How would I get all foos which had 10 or more bars (and therefore 10 or more cakes)?

Answer 1

Foo.all(:joins => :cakes, 
  :group => "cakes.foo_id", 
  :having => "count(cakes.bar_id) >= 10")