title: Zend Framework : Database find throws "Too few columns for the primary key" exception
body: <p>I am trying to use the <code>find</code> function to query the database table by id. The table has 4 primary keys (3 foreign keys).<br>
  This is the code of the table data gateway:  </p>
  
  <pre><code>class Application_Model_DbTable_Assigneduser extends Zend_Db_Table_Abstract
  {  
      protected $_name = 'assigneduser';  
  }  
  </code></pre>
  
  <p>This is the code of the Mapper:  </p>
  
  <pre><code>public function find($id)
  {
      $result = $this-&gt;getDbTable()-&gt;find($id);
      if(count($result) == 0)
          return;
      $row=$result-&gt;current();
      $assignedUser = new Application_Model_AssignedUser();
      $assignedUser-&gt;setId($row-&gt;id)
          -&gt;setIdProject($row-&gt;id_project)
          -&gt;setIdUser($row-&gt;id_user)
              -&gt;setIdTask($row-&gt;id_task);
  }  
  </code></pre>
  
  <p>The code I use to instantiate the mapper and where I use the method <code>find</code>:  </p>
  
  <pre><code>public function indexAction()
  {
          echo "&lt;xmp&gt;";
          $user=new Application_Model_AssignedUserMapper();
          print_r($user-&gt;find(3));
          echo '&lt;/xmp&gt;';
  }  
  </code></pre>
  
  <p>I used the <code>print_r</code> and <code>xmp</code> tag to have a good look at what the code returns.  The exception message I get is:  </p>
  
  <pre><code>Message: Too few columns for the primary key  
  </code></pre>
  
  <p>I have no idea what to do to fix it. Any idea? Thank you!</p>