more details about switch database function

[NacerKH]

Please i wanna more details how this function work

protected function setTenantConnectionDatabaseName(?string $databaseName)
 {
     $tenantConnectionName = $this->tenantDatabaseConnectionName();

     if ($tenantConnectionName === $this->landlordDatabaseConnectionName()) {
         throw InvalidConfiguration::tenantConnectionIsEmptyOrEqualsToLandlordConnection();
     }

     if (is_null(config("database.connections.{$tenantConnectionName}"))) {
         throw InvalidConfiguration::tenantConnectionDoesNotExist($tenantConnectionName);
     }

     config([
         "database.connections.{$tenantConnectionName}.database" => $databaseName,
     ]); here  i set the new configration 

     app('db')->extend($tenantConnectionName, function ($config, $name) use ($databaseName) {
         $config['database'] = $databaseName;

         return app('db.factory')->make($config, $name);
     });  why make an instance dbmanager with a new configuration even though I set it in config database file and i will purge=> disconnect and clear cache 

     DB::purge($tenantConnectionName);

     // Octane will have an old `db` instance in the Model::$resolver.
     Model::setConnectionResolver(app('db'));  why this even though i purge   mean ensure why the models will use the old config from cache 
 }   

thank you !