<p>
<?php
if (Yii::$app->$model->'id_guest') {
  echo Html::a('Download', ['download','id'=>$model->file_buku],['class'=>'btn btn-primary'] );
} elseif(Yii::$app->$model->identity->'id_guest') {
   echo  Html::button('Create Guest', ['value'=>Url::to('index.php?r=guest/create'),'class' => 'btn btn-success','id'=>'modalButton']) ;
}
?></p>