Select2 Widget

<?php
  $row = array();
  $query = ContactGroups::find();
  $conditions = ['group_status'=>'ACTIVE'];
    // default data when Insert Process / model are newRecord
  $data = ArrayHelper::map($query->where($conditions)->asArray()->all(),'group_id', 'group_name');
    // data return :
    // [
    //      "group_id"=>"group_name",
    //      "group_id"=>"group_name",
    //      "group_id"=>"group_name",
    //  ];
  if (!$model->isNewRecord)
  {
    $conditions = array_merge($conditions,['contact_contact_groups.contact_id'=>$model->contact_id]);
    $dataModel = ArrayHelper::map($query->joinWith('contactContactGroups')->where($conditions)->asArray()->all(),'group_id', 'group_name');
    foreach($dataModel as $k=>$d)
      $row[]=$k;
  }
?>

<div class="form-group field-contacts-group_id">
  <label class="col-sm-2 control-label" for="contacts-group_id">Group</label>
  <div class="col-sm-10">
    <?php
      echo Select2::widget([
          'name' => 'Contacts[group_id]',
          'value' => $row, //
          'data' => $data,
          'options' => ['placeholder' => 'Select a group ...', 'multiple' => true],
          'pluginOptions' => [
              'tags' => true,
              'maximumInputLength' => 10
          ],
      ]);
    ?>

  </div>
</div>