def set_default_left_and_right
      maxright = nested_set_scope.remove_order_by.max(right_field_name) || 0
      self[left_field_name] = maxright + 1
      self[right_field_name] = maxright + 2
      self[:depth] = 0
    end
def set_default_left_and_right
      maxright = nested_set_scope.remove_order_by.max(right_field_name) || 0
      self[left_field_name] = maxright + 1
      self[right_field_name] = maxright + 2
      self[:depth] = 0
    end
def set_default_left_and_right maxright = nested_set_scope . remove_order_by . max ( right_field_name ) || 0 self [ left_field_name ] = maxright + 1 self [ right_field_name ] = maxright + 2 self [ :depth ] = 0 end
on creation, set automatically lft and rgt to the end of the tree
on creation set automatically lft and rgt to the end of the tree