Preloading count of multiple named_scope in Rails

I have a the following classes

class Service < ActiveRecord::Base
    has_many :incidents
end

class Incident < ActiveRecord::Base
    belongs_to :service

    named_scope :active, lambda ...
    named_scope :inactive, lambda ...
end

I'm trying to preload the counts of each incidents class so that my view can do something like:

<% Service.all.each do |s| %>
    <%= s.active.count =>
    <%= s.inactive.count =>
<% end %>

Without making a SQL query for each count. 开发者_StackOverflow中文版I'm trying an approach with select but I'm not having much luck. Here's what I have so far:

# In Service class
def self.fetch_incident_counts
  select('services.*, count(incidents.id) as acknowledged_incident_count').
    joins('left outer join incidents on incidents.service_id = services.id').
    where('incidents.service_id = services.id AND ... same conditions as active scope').
    group('services.id')
end

That will prefetch one count, but I'm not sure how to do it for two different named_scope.

Using counter_cache is not an option because the database is being written to by non-rails code.

Any help welcome.

I ended up writing a gem for this. https://github.com/smathieu/preload_counts