Question

Given this class:

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

I know that when I set association1, it sets association1_id to the ID of object 1

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

I know that when I set association2, it sets association2_id AND association2_type

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

My question is:

Is there a function that can easily tell me what information is being set on an object in hash form?

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

Answer 1

This is the stop gap solution I have for now, just though I’d share:

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

Is this built into rails somewhere?