小编Nov*_*paX的帖子

这有什么问题before_save-callback？

class Order < ActiveRecord::Base

    has_many :line_items, :dependent => :destroy, :inverse_of => :order
    accepts_nested_attributes_for :line_items  
    attr_accessible :line_items_attributes


    before_save :mark_line_items_for_removal

    def mark_line_items_for_removal
      line_items.each do |line_item|
         line_item.mark_for_destruction if line_item.quantity.to_f <= 0
      end
    end
end

当其中之一line_items被标记为销毁时，line_item将不会保存。然而，父 Order 对象确实得到了保存。返回 true 并没有什么区别......

关于 mark_for_destruction：http ://apidock.com/rails/v3.1.0/ActiveRecord/AutosaveAssociation/mark_for_destruction 以及为什么不是“：allow_destroy => true”？见这里：http : //weblogs.manas.com.ar/spalladino/2010/03/15/deleting-children-with-accepts_nested_attributes_for-in-rails/

如果评估为false,Javascript中是否有一些速记来分配变量？

在红宝石中,我可以这样做:

foo |= "bar"

如果foo的计算结果为false,则将"bar"分配给foo,如下所示:(使用该| =运算符)

var cars_by_brand_and_color = {};
for (var car in parking_lot) {
   // add a brand if it doesn't exist yet;
   // cars_by_brand_and_color['chevrolet'] = {};
   cars_by_brand_and_color[car['brand']] |= {};
   // and add that color to the brand if it doesn't exist yet;
   // cars_by_brand_and_color['chevrolet']['grey'] |= {}; 
   cars_by_brand_and_color[car['brand']][car['color']] |= {};
   // now let's add that car; 
   // cars_by_brand_and_color['chevrolet']['grey']['BDB-565'] = 'Mr. Smith';
   cars_by_brand_and_color[car['brand']][car['color']][car['lisence_plate']] = car['owner']
};