change default db in cakephp3 - cakephp

Question

In a controller I want to change the default database so i can access the new db (db2) from anywhere in the website. The db2 database has the same models but just different data. My code just accesses the other database but doesnt set the new default database to db2 which can be accessed anywhere in the website. I didnt get the answer from the below posts.
This is my controller :
$connection = ConnectionManager::get('db2'); // 'db2' where my second database is configured
$results = $connection->execute('SELECT * FROM tutors')->fetchAll('assoc');
//this works but doesnt set the default database to db2 everywhere
This is my app.php :
'Datasources' => [
'default' => [
'className' => 'Cake\Database\Connection',
'driver' => 'Cake\Database\Driver\Mysql',
'persistent' => false,
'host' => 'localhost',
//'port' => 'non_standard_port_number',
'username' => 'root',
'password' => '',
'database' => 'aptutori_test',
'encoding' => 'utf8',
'timezone' => '+11:00',
'flags' => [],
'cacheMetadata' => true,
'log' => false,
'quoteIdentifiers' => false,
'url' => env('DATABASE_URL', null),
],
'db2' => [
'className' => 'Cake\Database\Connection',
'driver' => 'Cake\Database\Driver\Mysql',
'persistent' => false,
'host' => 'localhost',
//'port' => 'non_standard_port_number',
'username' => 'root',
'password' => '',
'database' => 'aptutori_testbak',
'encoding' => 'utf8',
'timezone' => '+11:00',
'flags' => [],
'cacheMetadata' => true,
'log' => false,
'quoteIdentifiers' => false,
'url' => env('DATABASE_URL', null),
],
Dynamically change database connection in cakephp 3
http://mark-story.com/posts/view/using-cakephp-and-a-horizontally-sharded-database

Answer 1

Use ConnectionManager::alias():
http://api.cakephp.org/3.0/class-Cake.Datasource.ConnectionManager.html#_alias
Fore example this will make all tables that require the default connection to use db2:
ConnectionManager::alias('db2', 'default');

Answer 2

You could do this application wide in a Middleware in > cake 3.3, opposed to using a DispatcherFilter, like described in http://mark-story.com/posts/view/using-cakephp-and-a-horizontally-sharded-database.
<?php
namespace App\Middleware;
use Cake\Datasource\ConnectionManager;
class TenantShardMiddleware
{
public function __invoke($request, $response, $next)
{
$tenant = $request->getHeader('MY-tenant');
ConnectionManager::alias($tenant[0], 'default');
$response = $next($request, $response);
return $response;
}
}
In my example above I'm using a special Request Header to switch databases.