CGridView search description instead value

Hi! I have two related entities, call them locality and zone. Locality belongs to a zone and zone has many localities.

I’ve setted all the relations and I have a CGridView inside the admin.php view as follow:

<?php $this->widget('zii.widgets.grid.CGridView', array(

	'id' => 'comune-grid',

	'dataProvider' => $model->search(),

	'filter' => $model,

	'columns' => array(



		'belongs_to_zone', /*name of the relations defined in Locality:relations() method*/		


			'class' => 'CButtonColumn',



)); ?>

all is working as expected, the column zone, infact, is populated with the description inside the zone table instead the numeric foreign key inside locality.

What is wrong is that if I try to insert a description inside the search text under the zone label nothing happens… The search for zone is broken. How can I fix it?