Magento 2 Connection to External Database

FishPig here. The tutorial on http://fishpig.co.uk/ is for M1 and is quite old (there are better ways connection to a DB on M1 than the tutorial says). Anyway, I've been trying to connect to an external DB while porting over Magento WordPress Integration to M2 so figured I'd post here what I have.

I'm not sure if this is the best way to do it but here's what I have that's working. Any feedback and improvements would be welcome!

<?php

namespace FishPig\SomeModule;

class App
{   
    protected $connectionFactory = null;

    public function __construct(
      \Magento\Framework\App\ResourceConnection\ConnectionFactory $connectionFactory
    ) {
        $this->connectionFactory = $connectionFactory;

        $this->_initDb();
    }

    protected function _initDb()
    {
        $db = $this->connectionFactory->create(array(
            'host' => 'localhost',
            'dbname' => 'enter_your_db_name',
            'username' => 'enter_your_db_username',
            'password' => 'enter_your_db_password',
            'active' => '1',    
        ));

        // Let's test the DB with a query

        $tableToTest = 'enter_your_table_name';

        $select = $db->select()
            ->from($tableToTest, '*');

        if ($results = $db->fetchAll($select)) {
            echo sprintf('<pre>%s</pre>', print_r($results, true));
        }
        else {
            echo 'The query was empty.';
        }
    }
}

This code uses DI to inject the \Magento\Framework\App\ResourceConnection\ConnectionFactory class. This works well because the class is a factory so doesn't instantiate the DB connection straight away. This allows you to gather the DB details and connect.

I should also point out that there are some values (DB details and DB table name for testing) that you will need to change for this code to work.

Database connection settings and backend name are declared in app/etc/config.php which was earlier declared in local.xml

1) In app/etc/env.php add this code:

'custom' => array (
      'host' => 'localhost',
      'dbname' => 'second_db_name',
      'username' => 'db_username',
      'password' => 'db_password',
      'engine' => 'innodb',
      'initStatements' => 'SET NAMES utf8;',
      'active' => '1',
),

And

'custom' => 
     array(
        'connection' => 'custom'
     ),

Final env.php file look like this:

  'db' => 
  array (
    'table_prefix' => '',
    'connection' => 
    array (
      'default' => 
      array (
        'host' => 'localhost',
        'dbname' => 'first_db_name',
        'username' => 'db_username',
        'password' => 'db_password',
        'active' => '1',
      ),
       'custom' => array (
          'host' => 'localhost',
          'dbname' => 'second_db_name',
          'username' => 'db_username',
          'password' => 'db_password',
          'engine' => 'innodb',
          'initStatements' => 'SET NAMES utf8;',
          'active' => '1',
      ),
    ),
  ),
  'resource' => 
  array (
    'default_setup' => 
    array (
      'connection' => 'default',
    ),
     'custom' => 
    array(
      'connection' => 'custom'
    ),
  ),

2) Next step is to configure resource model to use new connection. The di.xml configuration file of module will help to set new resource name to resource model. In Vendor/Module/etc/di.xml add this code:

<config xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:ObjectManager/etc/config.xsd">
    <type name="Vendor\Module\Model\ResourceModel\Module">
        <arguments>
           <argument name="connectionName" xsi:type="string">custom_setup</argument>
        </arguments>
    </type>
</config>