seach for STI grandchildren who are leaves

gistfile1.rb

# Computes STI models who are grandchildren or more.
#
# In a STI the root class and its subclasses work normally, but if there are
# grandchildren we need to preload them. Reason is, given A < B < C, if you
# for example compute B.count without loading A, only B records are taken into
# account in the query (where a clause about the type column intervenes). This
# is not a bug, Active Record is simply not aware of A. Once it is, the clause
# becomes an OR with all relevant types.
#
# I used this script to compute them.

ActiveRecord::Base.instance_eval do
  def concrete_superclass
    begin
      s = superclass
    end while s.abstract_class?
    s
  end
  
  def is_sti?
    concrete_superclass != ActiveRecord::Base
  end
  
  def is_sti_grandchild_or_more?
    is_sti? && concrete_superclass.is_sti?
  end
  
  def needs_preloading?
    is_sti_grandchild_or_more? && subclasses_of(self).empty?
  end
end

Dir["#{Rails.root}/app/models/**/*.rb"].each do |model|
  require_or_load model
end

puts subclasses_of(ActiveRecord::Base).
       select(&:needs_preloading?).
       map(&:name).
       sort