title: How to create a new record for a has many through association
body: <p>I have a list of checkboxes where people can select one or more organizations for a project. It's a has many through association.</p>
  
  <p>But I also want to add a text field that reads <code>Add Other</code> so the user can also create a new organization <strong><em>and assign it to the project automatically</em></strong>. </p>
  
  <p><strong>project.rb</strong></p>
  
  <pre><code>has_many :organizationables
  has_many :organizations, through: :organizationables
  attr_accessible :organization_ids
  </code></pre>
  
  <p><strong>organization.rb</strong></p>
  
  <pre><code>attr_accessible :name, :website
  has_many :organizationables
  has_many :projects, through: :organizationable
  </code></pre>
  
  <p><strong>organizationable.rb</strong></p>
  
  <pre><code>attr_accessible :organization_id, :project_id
  belongs_to :organization
  belongs_to :project
  </code></pre>
  
  <p>I know it's a weird name for the association 'organizationables` but oh well. I've tried different ways to setup the form but I can't make it work.</p>
  
  <p><strong>The NEW PROJECT FORM is supposed to have checkboxes where organizations can be assigned to a project but will also have a <code>Other Organization</code> text field (which will create a New Organization and assign it to the project).</strong> </p>