Virtual attributes on new models in Rails?

Question

Hi,

This certain part of my application takes cares of creation of Webshop model for store chains (like H&M) that has one. If the chain has a website that also is a webshop it creates one Webshop model.

If the website is not a webshop then it lets it be just at string in the Chain model.

PROBLEM: I'm doing this with a checkbox and virtual attributes. So when sending the a request to the chain controller a checkbox sets the value 'set_webshop'.

# Chain Model

class Chain
 has_one :webshop, :dependent => :destroy

 def set_webshop
  self.webshop.url == self.website unless self.webshop.blank?
 end

 def set_webshop=(value)
   if self.webshop.blank?
    value == "1" ? self.create_webshop(:url => self.website) : nil
   else
    value == "1" ? nil : self.webshop.destroy
   end
 end
end

# Chain Controller

class ChainsController < ApplicationController
  def create
    @chain = Chain.new(params[:chain])

    respond_to do |format|
      if @chain.save
        flash[:notice] = 'Chain was successfully created.'
        format.html { redirect_to(@chain) }
        format.xml  { render :xml => @chain, :status => :created, :location => @chain }
      else
        format.html { render :action => "new" }
        format.xml  { render :xml => @chain.errors, :status => :unprocessable_entity }
      end
    end
  end

  def update
    params[:chain][:brand_ids] ||= []
    @chain = Chain.find(params[:id])

    respond_to do |format|
      if @chain.update_attributes(params[:chain])
        flash[:notice] = 'Chain was successfully updated.'
        format.html { redirect_to(@chain) }
        format.js
      else
        format.html { render :action => "edit" }
      end
    end
  end
end

It all works perfectly when updating a Chain model but when not when creating a new one? I can't figure out why?

Here are the POST and PUT requests.

# POST (Doesn't work - does not create a Webshop)
Processing ChainsController#create (for 127.0.0.1 at 2010-02-06 11:01:52) [POST]
  Parameters: {"commit"=>"Create", "chain"=>{"name"=>"H&M", "set_webshop"=>"1", "website"=>"http://www.hm.com", "desc"=>"...", "email"=>"[email protected]"}, "authenticity_token"=>"[HIDDEN]"}


# PUT (Works - does create a Webshop)
Processing ChainsController#update (for 127.0.0.1 at 2010-02-06 11:09:13) [PUT]
  Parameters: { "commit"=>"Update", "chain"=> { "name" => "H&M", "set_webshop"=>"1", "website" => "http://www.hm.com", "desc" => "...", "email" => "[email protected]"}, "authenticity_token"=>"[HIDDEN]", "id"=>"444-h-m"}

Is there a special way to handle virtual_attributes on new models in Rails?

Answer 1

It probably doesn't work because in this line

self.create_webshop(:url => self.website)

to create a webshop for the new chain you have no id of the chain yet (it hasn't been created at this moment), so there's no possibility to create an association.

Define an after_save callback and create a webshop there. To remember the value of the checkbox in the meantime, you can store in an attr_accessor.