AR の名前付きスコープに相当するものはありますか? 名前付きスコープは基本的にフィルターであり、メソッドでラップしてチェーンすることができます。
http://archives.ryandaigle.com/articles/2008/8/20/named-scope-it-s-not-just-for-conditions-ya-knowの例を次に示します。
class Article < ActiveRecord::Base
# Get all articles that have been published
named_scope :published, :conditions => ['published = ?', true]
# Get all articles that were created recently
named_scope :recent, lambda { { :conditions => ['created_at >= ?', 1.week.ago] } }
end
# Get all recently created articles that have been published
Article.published.recent
Django ORM を使用した例を次に示します: http://furrybrains.com/2009/06/22/named-scopes-for-django/