Join a model with itself in Yii causes non-object error

Question

I have a model with these fields :

id , name , parent_id

I store a hirechical structure in this table.

somw example records are:

1 - fruits - 0
2 - foods -  0
3 - colors - 0
4 - apple -  1
5 - red -    3   
6 - meat-    2

In the gridview of manage(admin) page I want to show the parent name instead of its id. so I define this relation in the model (stuff).

public function relations()
{
  return array(
     'parent' => array(self::BELONGS_TO, 'stuff', 'parent_id'),
  );
}

and in view :

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

?>

But I get 'Trying to get property of non-object' error on admin page. It seems it is because of the root patents which their parent_id is '0' and there is no record with id=0 .

How can I deal with this problem?

Thanks you in advanced.

Answer 1

You have to add a check to the value expression

array(
    'name'=>'parent.name',
    'value'=>'($data->parent_id)?data->parent->name:""'
)

EDIT

For best practice you should leave parent_id blank instead of putting in a zero. If not every single time you want to access the parent using $model->parent you would have to perform the above check. Also for the grid parent.name could have been used instead of the above.

'name',
'parent.name',
array(
    'class'=>'CButtonColumn',
),