Rails的多個聯接AR查詢和where子句

Question

我有以下型號：

class Product < ActiveRecord::Base 
    has_many :product_recommendation_sets, :dependent => :destroy 
    has_many :recommendation_sets, :through => :product_recommendation_sets 
end 

class ProductRecommendationSet < ActiveRecord::Base 
    belongs_to :product 
    belongs_to :recommendation_set 
end 

class RecommendationSet < ActiveRecord::Base 
    has_many :product_recommendation_sets, :dependent => :destroy 
    has_many :products, :through => :product_recommendation_sets 

    has_many :recommendation_recommendation_sets, :dependent => :destroy 
    has_many :recommendations, :through => :recommendation_recommendation_sets 
end 

class RecommendationRecommendationSet < ActiveRecord::Base 
    belongs_to :recommendation 
    belongs_to :recommendation_set 
end 

class Recommendation < ActiveRecord::Base 
    has_many :recommendation_recommendation_sets, :dependent => :destroy 
    has_many :recommendations, :through => :recommendation_recommendation_sets 
end 

我試着去選擇所有recommendations其中的product_id = x，這樣做：

RecommendationSet.joins(:products, :recommendations).where(product_id:1) 

但是我得到一個未知列錯誤。我如何加入按給定的product_id選擇所有建議。 Psudo code： 查找recommendation_sets其中product_id = ?。查找recommendations，其中recommendation_set_id = ?。

Answer 1

你是八九不離十，你的情況這應該工作：

RecommendationSet.joins(:products, :recommendations).where(products: { id: 1 }) 

---

記住在where子句中，你必須在conditons哈希值，而不是使用表的名稱關係的名字。

爲例，考慮這些關係：

User belongs_to :group 
Group has_many :users 

通知語法（複數/單數）：

User.joins(:group).where(groups: { name: 'Admin' }) 
#    ^   ^
Group.joins(:users).where(users: { id: 15 }) 
#    ^  ^