检查负载SQL对象在Rails的

Question

我的模型：

class User 
    has_many :items 
end 

class Item 
    belongs_to :user 

    def self.with_color(color, is_loaded) 
    if is_loaded 
     self.select { |i| i.color == color } 
    else 
     self.where(:color => color) 
    end 
    end 

end 

有我的控制器2种类型的代码。

## this line loads 'items' of the user and selects with the red color ## 
@colored_items = current_user.items.with_color('red', false) 

## this code should not load items twice ## 
@user_with_items = User.includes(:items).find(params[:user_id]) 
(...) 
colored_items = @user_with_items.with_color('red', true) 

如果我只写“选择”的版本，它不与1例如工作，和“地点”版本加载项再次即使它们已经加载。

如何检查对象是否已经加载？

Answer 1

如何使用范围？

从例子摘自：

class Shirt < ActiveRecord::Base 
    scope :colored, lambda { |color| where(:color => color) } 
end 

更多阅读这里：http://apidock.com/rails/ActiveRecord/Scoping/Named/ClassMethods/scope

你的榜样，这应该是（未测试）

class User 
    has_many :items 
end 

class Item 
    belongs_to :user 
    scope :colored, lambda { |color| where(:color => color) } 
end 


## this line loads 'items' of the user and selects with the red color ## 
@colored_items = current_user.items.colored('red') 

## use of 'includes' here to solve (n+1) issue 
@user_with_items = User.includes(:items).find(params[:user_id]) 
colored_items = @user_with_items.colored('red') 

更新：

class User < ActiveRecord::Base 
    has_many :items 

    def colored_items(color) 
    self.items.to_a.select { |i| i.color == color } 
    end 
end 

user = User.includes(:items).find(1) 
    User Load (0.2ms) SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1 [["id", 1]] 
    Item Load (0.4ms) SELECT "items".* FROM "items" WHERE "items"."user_id" IN (1) 
=> #<User id: 1, name: nil, created_at: "2012-03-25 00:39:52", updated_at: "2012-03-25 00:39:52"> 
user.colored_items "red" 
=> [#<Item id: 1, color: "red", user_id: 1, created_at: "2012-03-25 00:41:00", updated_at: "2012-03-25 00:41:00">] 
user.colored_items "blue" 
=> [#<Item id: 2, color: "blue", user_id: 1, created_at: "2012-03-25 00:41:04", updated_at: "2012-03-25 00:41:04">] 

所以这里只有2个SQL。