// Node: has many NodeDropIns. Relation set in schema.yml
// NodeDropIn: has one DropIn. Relation set below.
// Dropin: pseudo-model, currently have HtmlDropIn and YoutubeDropIn models (text column in NodeDropIn)

    foreach ($this->NodeDropIns as $i => $node_drop_in) {

      if (!in_array($node_drop_in->drop_in, $drop_ins_added)) {
          $drop_ins_added[] = $node_drop_in->drop_in;

          $node_drop_in->hasOne(
            $node_drop_in->getDropInObject()->getModel() . ' as DropIn',
            array(
              'local'   => 'drop_in_id',
              'foreign' => 'id'
            )
          );

          $query = $query->leftJoin(
              sprintf('di.DropIn d__%d ON d__%d.id = di.drop_in_id AND di.drop_in = \'%s\'', $i, $i, $node_drop_in->drop_in)
          );
      }