title: MM relation which is added with command controller not shown in backend field
body: <p>I've experienced some issues with adding mm relations via a command controller in TYPO3.</p>
  <p>I've tried to migrate the author field of pages (which is normally a varchar field in order to fill a string) to a mm relation of fe_users. In my database the mm relations are added correctly, but in the backend the selected fe_users are not shown in the author field.</p>
  <p>I've tried to add them via a datahandler script in a command controller (I've also tried to add them with a query builder before, but same problem):</p>
  <pre><code>/**
   * @var array
   */
  protected $mappingUsers = [
      'Max Mustermann' =&gt; 2,
      'Miri Musterfrau' =&gt; 5
  ];
  
  public function execute(InputInterface $input, OutputInterface $output)
  {
      /** @var ConnectionPool $connectionPool */
      $connectionPool = GeneralUtility::makeInstance(ConnectionPool::class);
  
      /** @var QueryBuilder $queryBuilderPages */
      $queryBuilderPages = $connectionPool-&gt;getQueryBuilderForTable('pages');
  
      /** @var QueryBuilder $queryBuilderAuthor */
      $queryBuilderAuthor = $connectionPool-&gt;getQueryBuilderForTable('tx_project_pages_author_mm');
  
      $pages = $queryBuilderPages
          -&gt;from('pages')
          -&gt;select('*')
          -&gt;execute()
          -&gt;fetchAll();
  
      /** @var DataHandler $dataHandler */
      $dataHandler = \TYPO3\CMS\Core\Utility\GeneralUtility::makeInstance(\TYPO3\CMS\Core\DataHandling\DataHandler::class);
      $data = [];
  
      foreach ($pages as $page) {
          if ($page['author']) {
              foreach ($this-&gt;mappingUsers as $key =&gt; $value) {
                  if ($page['author'] === $key) {
                      $data = [
                          'pages' =&gt; [
                              $page['uid'] =&gt; [
                                  'author' =&gt; $value,
                                  'tstamp' =&gt; time(),
                              ]
                          ],
                          'tx_project_pages_author_mm' =&gt; [
                              str_replace(' ', '', 'NEW' . microtime() . rand()) =&gt; [
                                  'uid_local' =&gt; $page['uid'],
                                  'uid_foreign' =&gt; $value
                              ]
                          ]
                      ];
  
                      $dataHandler-&gt;start($data, []);
                      $dataHandler-&gt;process_datamap();
  
                      unset($data);
                  }
              }
          }
      }
  
      $queryBuilderPages
          -&gt;update('pages')
          -&gt;where(
              $queryBuilderPages-&gt;expr()-&gt;eq('author', &quot;''&quot;),
          )
          -&gt;set('author', 0)
          -&gt;execute();
  
      return 0;
  }
  </code></pre>
  <p>Is there anything else to do after adding mm relations via a command controller?</p>