如何使用纯 activerecord (rails) 执行此 sql

Question

我不知道如何纯粹使用活动记录来管理它。我知道它不处理外连接...

SQL：

SELECT * FROM people 
LEFT OUTER JOIN responses 
ON people.id = responses.person_id 
WHERE responses.person_id is NULL;

模型：

Person
id
has_many :responses

Response
id
belongs_to :person

有什么建议吗？

Answer 1

named_scope :without_responses, :include    => :responses, 
                                :conditions => "responses.id IS NULL"