gistfile1.txt

class Employee < ActiveRecord::Base
end

class Manager < Employee
  self.table_name = 'employees'
  has_many :engineers

  def nearest_manager
    self
  end
end

class Engineer < Employee
  self.table_name = 'employees'
  belongs_to :nearest_manager, class_name: 'Manager'
end

# want to be able to say:
Employee.all.includes(:nearest_manager)

# ... and get back a collection of mixed Manager and Employee instances, where
# the nearest_manager method on Managers just returns self, and the
# nearest_manager association on Engineers is preloaded using a single batch SQL
# query

Is there a nearest_manager_id column? If so, could you not do

class Manager < Employee
  self.table_name = 'employees'
  has_many :engineers

  belongs_to :nearest_manager, class_name: 'Manager'
  # I think this will work if you set this manager's nearest_manager_id to its own id.
end