Ruby on rails 检查Rails中是否加载了sql对象

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

我的控制器中有两种类型的代码

## 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)

如果我只写选择版本，它不适用于1个示例，“where”版本再次加载项目，即使它们已经加载

---

如何检查对象是否已加载？

如何使用作用域

例如：

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

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。

Scope与self.colored的方法相同。第一个示例运行良好，但第二个示例将执行另一个查询，以仅加载“红色”项。我会使用@users_with_items.items.select{| e | e.color=='red'}而不是scope来使用已经加载的对象。好的，你说得对。Scope每次都在执行SQL。我想它会处理好的。可能是可以优化的东西。所以我在上面的答案中添加了一个可能的解决方案。谢谢-。正是我需要的。

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">]