导轨 - 确定什么一个对象的属性是由一个二传手

Question

鉴于这种类设置：

class MyModel < ActiveRecord::Base 
    belongs_to :association1 
    belongs_to :association2, :polymorphic => true 
end 

我知道，当我设置association1，它设置association1_id到对象的ID 1

m = MyModel.new 
m.association1 = object1 
#<MyModel id: nil, association1_id: 1, association2_id: nil, association2_type: nil> 

我知道，当我设置association2，它集association2_id和association2_type

m.association2 = object2 
#<MyModel id: nil, association1_id: 1, association2_id: 2, association2_type: 'ClassType'> 

我的问题是：

是否有一个函数可以很容易地告诉我什么信息以散列形式设置在一个对象上？

MyModel.magic_function(:association1, object1) 
# returns {:association1_id => 1} 
MyModel.magic_function(:association2, object2) 
# returns {:association2_id => 2, :association2_type => 'ClassType'} 

Answer 1

这是权宜的解决方案我现在，只是虽然我会分享：

def self.magic_method(association, object) 
    instance = self.new 
    instance.send(association, object) 
    h = Hash.new 
    instance.changes.each do |k,v| 
    h[k] = v[1] 
    end 
    h 
end 

这是内置到铁轨的地方？

Answer 2

也许你正在寻找changes：

person = Person.new 
person.changes # => {} 
person.name = 'bob' 
person.changes # => { 'name' => [nil, 'bob'] }