導軌 - 確定什麼一個對象的屬性是由一個二傳手

Question

鑑於這種類設置：

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

我知道，當我設置association1，它設置association1_id到對象的ID 1

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

我知道，當我設置association2，它集association2_id和association2_type

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

我的問題是：

是否有一個函數可以很容易地告訴我什麼信息以散列形式設置在一個對象上？

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

Answer 1

這是權宜的解決方案我現在，只是雖然我會分享：

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 

這是內置到鐵軌的地方？

Answer 2

也許你正在尋找changes：

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