I believe it is easier when you just create your own dropdown list provider
in the Employee.php you add these two functions:
public function getFullName()
{
return $this->first_name.' '.$this->last_name; // or what ever you want to be shown on the drop list
}
public static function getNamesList() {
return CHtml::listData(self::model()->findAll(), 'idEmployee', 'fullName');
}
in the _FORM.php write:
<div class="row">
<?php echo $form->labelEx($model,'idEmployee'); ?>
<?php echo $form->dropDownList($model, 'idEmployee', Employee::getNamesList()); ?>
<?php echo $form->error($model,'idEmployee'); ?>
</div><!-- row -->