ruby-on-rails - find_by_sql 不返回额外的属性

Question

我正在使用 find_by_sql 对这样的关系进行左连接计数:

scope :popular, lambda{ |since_date = false| 
      query = "select l.*, count(c.id) as popular_count from lists l left join choice_sets c on c.list_id = l.id and c.set_type = 'user'"
      query << "and c.updated_at > " + since_date.strftime("'%Y-%m-%d %H:%M:%S'") if since_date
      query << " group by l.id order by popular_count asc"
      find_by_sql(query)
  }

我遇到了返回数据的问题，不包括属性散列中的额外属性 popular_count:

>  List.popular.first.attributes.keys
=> ["id", "name", "listtype", "slug", "description", "created_at", "updated_at", "user_id"] 

我相信我应该能够访问此属性散列中的 popular_count？我正在使用 postgres。

Answer 1

我可以在 Rails 3.2(而不是 Rails 4)上重现这个问题

我在 app/models/list.rb 中有一个名为 popular 的作用域和一个名为 pop 的类方法:

class List < ActiveRecord::Base
  scope :popular, lambda{ |since_date = false| 
    query = "select l.*, count(l.id) as popular_count from lists l "
    query << "and l.updated_at > " + since_date.strftime("'%Y-%m-%d %H:%M:%S'") if since_date
    query << " group by l.id order by popular_count asc"
    self.find_by_sql(query)
}

  def self.pop
    since_date = false
    query = "select l.*, count(l.id) as popular_count from lists l "
    query << "and l.updated_at > " + since_date.strftime("'%Y-%m-%d %H:%M:%S'") if since_date
    query << " group by l.id order by popular_count asc"
    find_by_sql(query)
  end

结束

在控制台中，popular 没有 popular_count 作为属性:

2.0.0-p353 :002 > List.popular.first.attributes.keys

List Load (0.2ms) select l.*, count(l.id) as popular_count from lists l group by l.id order by popular_count asc

List Load (0.1ms) SELECT "lists".* FROM "lists"

=> ["id", "name", "created_at", "updated_at"]

虽然类方法 pop 做:

2.0.0-p353 :001 > List.pop.first.attributes.keys

List Load (0.6ms) select l.*, count(l.id) as popular_count from lists l group by l.id order by popular_count asc

=> ["id", "name", "created_at", "updated_at", "popular_count"]

因此，如果无法使用 Rails 4，我建议使用类方法作为解决方法。