exists instead of inner join?

[Brad Langhorst]

I need to set permission on an object based on whether a there exists an object in a has many relationship with a specific property value.

    has_permission_on :conditions, :to => [:new, :create,:update,:read,:show,:index] do

      if_permitted_to :read, :experimental_conditions

      #if_attribute :experimental_conditions =>{ :well_id => is { nil }}

    end

    has_permission_on :experimental_conditions, :to => [:new, :create,:update,:read, :show, :index] do

      if_attribute :well_id => is { nil }

    end

Condition.with_permissions_to(:read).all sort of works... but it creates this sql.

SELECT "conditions".* FROM "conditions" INNER JOIN "experimental_conditions" ON "experimental_conditions"."condition_id" = "conditions".id WHERE (("experimental_conditions"."well_id" IS NULL)) 

This would be better, since it would not return a bunch of un-needed data and would be faster.

SELECT "conditions".* FROM "conditions" where exists (select 1 from  "experimental_conditions" WHERE  "experimental_conditions"."condition_id" = "conditions".id AND (("experimental_conditions"."well_id" IS NULL)) )

I don't see how to do this with d-a. Is it possible?

Is it worth extending rebuild_condition_options to do this?

I don't see immediately how to do it, but i think it's possible.

Thanks!

Brad