class ActiveRecord::Reflection::ThroughReflection

def check_validity!
  if through_reflection.nil?
    raise HasManyThroughAssociationNotFoundError.new(active_record, self)
  end
  if through_reflection.polymorphic?
    if has_one?
      raise HasOneAssociationPolymorphicThroughError.new(active_record.name, self)
    else
      raise HasManyThroughAssociationPolymorphicThroughError.new(active_record.name, self)
    end
  end
  if source_reflection.nil?
    raise HasManyThroughSourceAssociationNotFoundError.new(self)
  end
  if options[:source_type] && !source_reflection.polymorphic?
    raise HasManyThroughAssociationPointlessSourceTypeError.new(active_record.name, self, source_reflection)
  end
  if source_reflection.polymorphic? && options[:source_type].nil?
    raise HasManyThroughAssociationPolymorphicSourceError.new(active_record.name, self, source_reflection)
  end
  if has_one? && through_reflection.collection?
    raise HasOneThroughCantAssociateThroughCollection.new(active_record.name, self, through_reflection)
  end
  if parent_reflection.nil?
    reflections = active_record.reflections.keys.map(&:to_sym)
    if reflections.index(through_reflection.name) > reflections.index(name)
      raise HasManyThroughOrderError.new(active_record.name, self, through_reflection)
    end
  end
  check_validity_of_inverse!
end