admin.php

<?php $this->widget('zii.widgets.grid.CGridView', array(
    'id' => 'hoge-grid',
    'dataProvider' => $model->search(),
    'filter' => $model,
    'columns' => array(
        'id',
        array(
            'name' => 'username',
            'value' => '$data->user->username',
        ),
        'fuga',
        'piyo',
        array(
            'class' => 'CButtonColumn',
        ),
    ),
)); ?>