Example of how to determine if a class method is defined on the current class or an ancestor. Notice that Method#owner returns the metaclass, so we can't just compare to the class itself.

establish_connection.rb

base_classes_with_own_connection = ActiveRecord::Base.subclasses.find_all { |klass|
  klass.method(:establish_connection).owner == (class << klass; self; end)
}
([ActiveRecord::Base] + base_classes_with_own_connection).each do |base|
  base.establish_connection
end

Alternative predicate:

(class << klass; self; end).instance_methods(false).include?(:establish_connection)