How will i get purchase_order_name from this type of data in yii2

common\models\Section Object
(
[_attributes:yii\db\BaseActiveRecord:private] => Array
(
[section_id] => 4
[section_name] => VLP2_UTILITY
[location_id] => 4
[state_id] => 1
[plant_id] => 5
[po_id] => 2
[is_delete] => 0
[created_at] => 2021-09-03 07:34:19
[updated_at] => 2021-09-06 10:09:03
)

[_oldAttributes:yii\db\BaseActiveRecord:private] => Array
    (
        [section_id] => 4
        [section_name] => VLP2_UTILITY
        [location_id] => 4
        [state_id] => 1
        [plant_id] => 5
        [po_id] => 2
        [is_delete] => 0
        [created_at] => 2021-09-03 07:34:19
        [updated_at] => 2021-09-06 10:09:03
    )

[_related:yii\db\BaseActiveRecord:private] => Array
    (
        [po] => common\models\Purchaseorder Object
            (
                [_attributes:yii\db\BaseActiveRecord:private] => Array
                    (
                        [po_id] => 2
                        [purchase_order_name] => VLP2_UTILITY_O_M
                        [location_id] => 4
                        [state_id] => 1
                        [plant_id] => 5
                        [is_delete] => 0
                        [created_at] => 2021-09-03 07:34:07
                        [updated_at] => 2021-09-06 10:09:01
                    )

                [_oldAttributes:yii\db\BaseActiveRecord:private] => Array
                    (
                        [po_id] => 2
                        [purchase_order_name] => VLP2_UTILITY_O_M
                        [location_id] => 4
                        [state_id] => 1
                        [plant_id] => 5
                        [is_delete] => 0
                        [created_at] => 2021-09-03 07:34:07
                        [updated_at] => 2021-09-06 10:09:01
                    )

                [_related:yii\db\BaseActiveRecord:private] => Array
                    (
                    )

                [_relationsDependencies:yii\db\BaseActiveRecord:private] => Array
                    (
                    )

                [_errors:yii\base\Model:private] => 
                [_validators:yii\base\Model:private] => 
                [_scenario:yii\base\Model:private] => default
                [_events:yii\base\Component:private] => Array
                    (
                    )

                [_eventWildcards:yii\base\Component:private] => Array
                    (
                    )

                [_behaviors:yii\base\Component:private] => Array
                    (
                    )

            )

    )

[_relationsDependencies:yii\db\BaseActiveRecord:private] => Array
    (
    )

[_errors:yii\base\Model:private] => 
[_validators:yii\base\Model:private] => 
[_scenario:yii\base\Model:private] => default
[_events:yii\base\Component:private] => Array
    (
    )

[_eventWildcards:yii\base\Component:private] => Array
    (
    )

[_behaviors:yii\base\Component:private] => Array
    (
    )

)

$sectionModel->po->purchase_order_name;
if array
$sectionModel['po']['purchase_order_name'];

If $sectionModel is multiple then loop through it.