How to retrieve the column from relation in YII2 - yii2-advanced-app

Question

I am using ajax to call a method from the server that returns a string data. However I get the following error.
PHP Notice 'yii\base\ErrorException' with message 'Trying to get
property of non-object'
probably this line $first_day=$row->tblStaff2->first_day_service; gives the error.
public function actionGet_loyalty() {
$model = \common\models\staffs\TblStaff::find()->joinWith('tblStaff2')->all();
$string = "<table class='table table-striped'><tr><th>Name</th><th>Number of Years</th></tr>";
foreach ($model as $row) {
$first_day=$row->tblStaff2->first_day_service;
$midname = ucwords($row->midname);
$name = ucwords($row->firstname) . " " . $midname[0] . ". " . ucwords($row->lastname);
$string.="<tr>"
. "<td>" . $name . "</td>"
. "<td>" . $first_day . "</td>"
. "</tr>";
}
$string.="</table>";
return $string;
}
TblStaff relation
public function getTblStaff2() {
return $this->hasOne(TblStaff2::className(), ['staff_id' => 'id']);
}

Answer 1

I have modified your code. Find it below
public function actionGet_loyalty() {
$model = \common\models\staffs\TblStaff::find()->all();
$string = "<table class='table table-striped'><tr><th>Name</th><th>Number of Years</th></tr>";
foreach ($model as $row) {
//What I added
foreach($row->tblStaff2 as $value){
$first_day = $value->first_day_service;
//Here is where it stopped
$midname = ucwords($row->midname);
$name = ucwords($row->firstname) . " " . $midname[0] . ". " . ucwords($row->lastname);
$string.="<tr>"
. "<td>" . $name . "</td>"
. "<td>" . $first_day . "</td>"
. "</tr>";
}
}
$string.="</table>";
return $string;
}
You can remove the comments i added to it when you get it working.