How to update a model's attribute with a virtual attribute? - ruby-on-rails

Question

I have a model named UserPrice which has the attribute :purchase_date(a date_select) in its table. With my form I can create multiple user_prices at once but for user convenience I made a virtual attribute inside of my UserPrice model called :all_dates that's also a date_select field and its job is to be the replacement of the :purchase_dates so users only have to select the :all_dates field for the date.
Problem & Question
The :all_dates field is not updating the :purchase_date fields of my user_prices that are being created. What do I need to do in order to get my :all_dates field to update the :purchase_date fields of my new UserPrices?
Does anyone have any tips on how to do this?
Parameters
Parameters:
"user_price"=> {
"all_dates(2i)"=>"10",
"all_dates(3i)"=>"27",
"all_dates(1i)"=>"2011"
},
"user_prices"=>
{
"0"=>{"product_name"=>"Item1", "store"=>"Apple Store","price"=>"6"},
"1"=>{"product_name"=>"Item2", "store"=>"Apple Store", "price"=>"7"}
},
"commit"=>"Submit"}
Code
class CreateUserPrices < ActiveRecord::Migration
def self.up
create_table :user_prices do |t|
t.decimal :price
t.integer :product_id
t.date :purchase_date
t.timestamps
end
end
end
I took out the :purchase_date field so it isn't inside of the user_price loop.
<%= form_tag create_multiple_user_prices_path, :method => :post do %>
<%= date_select("user_price", "all_dates" ) %>
<% #user_prices.each_with_index do |user_price, index| %>
<%= fields_for "user_prices[#{index}]", user_price do |up| %>
<%= render "user_price_fields", :f => up %>
<% end %>
<% end %>
<% end %>
class UserPrice < ActiveRecord::Base
attr_accessible :price, :product_name, :purchase_date, :all_dates, :store
attr_accessor :all_dates
after_save :save_all_dates_to_user_prices
composed_of :all_dates, :class_name => "DateTime",
:mapping => %w(Time to_s),
:constructor => Proc.new { |item| item },
:converter => Proc.new { |item| item }
def user_prices
#user_prices = Array.new() { UserPrice.new }
end
protected
def save_all_dates_to_user_prices
if !self.all_dates.nil?
self.user_prices.each {|up| up.purchase_date = self.all_dates if up.new_record?}
end
end
class UserPricesController < ApplicationController
def new
#user_prices = Array.new(5) { UserPrice.new }
end
def create_multiple
#user_prices = params[:user_prices].values.collect { |up| UserPrice.new(up) }
if #user_prices.all?(&:valid?)
#user_prices.each(&:save!)
redirect_to :back, :notice => "Successfully added prices."
else
redirect_to :back, :notice => "Error, please try again."
end
end

Answer 1

This is a case of trying to do in a model what is better left to the controller. All you're trying to do here is to auto-assign a certain attribute on creation from a parameter not directly tied to your model. But you're not even passing that extra parameter to the model anywhere - you're creating your model instances from the user_prices parts of the parameter hash, but the user_price sub-hash is not used anywhere. In any case, this is behavior that is more closely related to the view and action taken than the model, so keep it in the controller.
Try this:
Throw out the virtual attribute, and get rid of the whole after_save callback stuff
Throw away the user_prices method in your model
Change the all_dates attribute name back to purchase_date in the form
Then your parameter hash should look like this:
{"user_price"=> {
"purchase_date(2i)"=>"10",
"purchase_date(3i)"=>"27",
"purchase_date(1i)"=>"2011"
},
"user_prices"=>
{
"0"=>{"product_name"=>"Item1", "store"=>"Apple Store","price"=>"6"},
"1"=>{"product_name"=>"Item2", "store"=>"Apple Store", "price"=>"7"}
}}
All that's left to do is to merge the single user_price attributeS into each user_prices sub-hash in your create_multiple action. Replace the first line in that action with this:
#user_prices = params[:user_prices].values.collect do |attributes|
UserPrice.new(attributes.merge(params[:user_price]))
end

Answer 2

I'm not sure why you are even using that virtual attribute is there more to this implementation? If you are just trying to save an associated model, you might simply want a accepts_nested_attributes_for :user_prices in your User model
This works great and many developers use this method, so it's nice to know for working on other projects as well as for the people who might end up maintaining yours.
http://railscasts.com/episodes/196-nested-model-form-part-1
http://railscasts.com/episodes/197-nested-model-form-part-2