title: rails: create Parent, if doesn't exist, whilte creating child record
body: <p>Any best practices for the following?:</p>
  
  <p>I have Manufacturer model that has_many Inventory</p>
  
  <p>In my new Inventory form I want a field that maps to Manufacturer.name so that when one 
  submits the new Inventory form the app:</p>
  
  <ul>
  <li>searches for a manufacturer with the 'name' from the form
  
  <ul>
  <li>if it exists then assign the id to @inventory.manufacturer_id and save @inventory</li>
  <li>if it doesn't exist then create the manufacturer with the 'name' from the form, assign the id to @inventory.manufacturer_id and save</li>
  <li>have validations work on the new Inventory form
  
  <ul>
  <li>such that, if the the Inventory form fails validation on a field other than 'name'
  
  <ul>
  <li>the 'name' field will be repopulated with whatever the user entered (but a new manufacturer is not created unless the form passes validation)</li>
  </ul></li>
  </ul></li>
  </ul></li>
  </ul>