Yii2 change default Route to another namespace - php

Question

the default route in Yii2 is #app/controllers/SiteController.
but If I build from beginning.
composer require yiisoft/yii2
then I create my own index.php and set the configure for the app
(new yii\web\Application($config))->run();
and the application is always try to local the defaultContoller in the app namespace. but If i put the SiteController in another namespace. it gives me 404 error,
index.php
require(__DIR__ . '/vendor/autoload.php');
require(__DIR__ . '/vendor/yiisoft/yii2/Yii.php');
$config = require(__DIR__ . '/repo/config/web.php');
(new yii\web\Application($config))->run();
web.php
'id' => 'repo',
'basePath' => dirname(__DIR__),
'controllerNamespace' => 'repo\\controllers',
'defaultRoute' => 'site/index',
folder structure
/vendor
-yiisoft
/repo
-config
---web.php
-controllers
---SiteController.php
SiteController.php
<?php
namespace repo\controllers;
use Yii;
use yii\web\Controller;
class SiteController extends Controller{
public function actionIndex(){
echo 'welcome to the site';
}
}
?>
if I give the SiteController.php namespace app/controllers it works,but once I change it back to repo/controllers it says page not found.

Answer 1

try this in you config file:
'controllerNamespace' => 'newnamespace\controllers',
'defaultRoute' => 'new/index',

Answer 2

yii\base\Application object has a public property controllerNamespace, which defaults to app\\controllers, you need to change it accordingly to changing default controller namespace.
Add this to your application config:
[
...
'controllerNamespace' => 'app\\other\\namespace\controllers',
...
],
Default route is site (for yii\web\Application), it can be changed the same way (defaultRoute property):
[
...
'defaultRoute' => 'otherDefaultRoute',
...
],

Answer 3

I found I forgot to define the root alias.
// $className is a fully qualified class name without the leading backslash
$classFile = Yii::getAlias('#' . str_replace('\\', '/', $className) . '.php');
so If I define the root alias #repo in the configuration. then it works
'aliases' => [
'#repo' => dirname(__DIR__),
],