rails：無法從連接表中獲取屬性

Question

當我連接兩個表（rails 2.2.2）時，rails僅返回應用了find_by方法的模型中的屬性值：

關係：

class User < ActiveRecord::Base 
    .. 
    has_one :company_info, :dependent => :destroy 
    has_many :preferred_categories, :dependent => :destroy 
end 


class PreferredCategory < ActiveRecord::Base 
    .. 
    belongs_to :user 
    belongs_to :category 

end 


class Category < ActiveRecord::Base 
    .. 
    has_many :preferred_categories, :dependent => :destroy 
    has_many :users, :through => :preferred_categories 
end 


class CompanyInfo < ActiveRecord::Base 
    .. 
    belongs_to :user 
end 

查詢：

class Category < ActiveRecord::Base 
    .. 
    def total_tradesmen #returns tradesmen with a certain skill-profile 
    a = self.self_and_all_children_for.collect {|cat| cat.id} 
    total_tradesmen = User.find_by_sql(
    "select * 
    from users u 
    inner join preferred_categories pc on pc.user_id = u.id 
    inner join company_infos ci on ci.user_id = pc.user_id 
    where pc.category_id in (#{a.join(',')})" 
) 
    end 
.. 
end 

=>結果：我從用戶表僅屬性。

我需要的是來自其他表（preferred_categories，company_infos）的屬性。有任何想法嗎？

Answer 1

在你的情況下，我認爲ActiveRecord可以處理你的查詢。您應該使用include加載您需要的關聯。

total_tradesmen = User.all(
    :include => [:company_info, :preferred_categories], 
    :conditions => {:preferred_categories => {:category_id => a}} 
) 

然後訪問相關的模型，你需要的屬性：

# Examples since I don't know the attributes on your models 
company_address = total_tradesmen.first.company_info._address_ 
preferred_category_names = total_tradesmen.first.preferred_categories.map(&:_name_) 

UPDATE 嘗試指定連接明確

total_tradesmen = User.all(
    :include => [:company_info, :preferred_categories], 
    :joins => [:company_info, :preferred_categories], 
    :conditions => {:preferred_categories => {:category_id => a}} 
)