How to update two tables from one form yii

How to update two tables from one form yii

I have to update two tables from one form. I have two tables TestA and
TestB. So how can I update two tables where TestB.testid=TestA.testid.
Both the tables are populated. I need to update TestB based on the id of
TestA. Below is the actionUpdate of TestA.
public function actionUpdate($id)
{ $model_A=new TestA;
$model_B=new TestB;
$model=$this->loadModel($id);
if(isset($_POST['TestA'])&&isset($_POST['TestB']))
{
$model_A->attributes=$_POST['TestA'];
$model_B->attributes=$_POST['TestB'];
$model_B->name="test";
$model_A->save();
$model_B->save();
$this->render('update',array(
'model'=>$model,
));
}
When I run the application, a new entry is created in TestB instead of
updating the existing one. How can I pass the id to update the row in
table TestB