'btn btn-success']) ?>

$dataProvider, 'filterModel' => $searchModel, 'columns' => [ ['class' => 'yii\grid\SerialColumn'], [ 'attribute' => 'user_id', 'filter' => User::find()->select(['username', 'id'])->indexBy('id')->column(), 'value' => 'user.username', ], ['class' => 'yii\grid\ActionColumn'], ], ]); ?>