title: Many-To-Many with additional parameters
body: <p>using the default entity creation commands:</p>
  
  <pre><code>php app/console doctrine:mapping:import testSiteBundle yml
  php app/console doctrine:generate:entities test --path=src/
  </code></pre>
  
  <p>Can i make additional parameters in many-to-many relation table work with symfony2+doctrine2 ?</p>
  
  <p>Example case:</p>
  
  <pre><code>Table Invoice
    - invoice id
  Table Product
    - product id
  Relation-Table InvoiceProduct
    - invoice id
    - product id
    - product quantity
  </code></pre>
  
  <p>Doctrine by default don't create relation-tables entities, and trying the example above, the "product quantity" is ignored.</p>
  
  <p>what can i do to manage this?</p>