SilverStripe database setup on Heroku.

composer.json

{
	"name": "silverstripe/installer",
	"description": "The SilverStripe Framework Installer",
	"require": {
		"ext-gd": "*",
		"ext-mbstring": "*",
		"silverstripe/cms": "3.1.*@stable",
		"silverstripe/framework": "3.1.*@stable",
		"silverstripe-themes/simple": "*"
	},
	"require-dev": {
		"phpunit/PHPUnit": "~3.7@stable"
	},
	"config": {
		"process-timeout": 600
	},
	"minimum-stability": "dev"
}

SilverStripe on Heroku

mysite/_config.php
<?php
// . . . config above
//Heroku ClearDB support
if(isset($_ENV['CLEARDB_DATABASE_URL'])) {
	global $databaseConfig;
	$parts = parse_url($_ENV['CLEARDB_DATABASE_URL']);
	$databaseConfig['type'] = 'MySQLDatabase';
	$databaseConfig['server'] = $parts['host'];
	$databaseConfig['username'] = $parts['user'];
	$databaseConfig['password'] = $parts['pass'];
	$databaseConfig['database'] = trim($parts['path'], '/');
	Security::setDefaultAdmin('heroku', 'yesletmeinplease');
} else {
	//Default SilverStripe environement support
	require_once('conf/ConfigureFromEnv.php');
}

// Config below . . .

This was handy @camfindlay ... your composer.json configs helped ... I think it just needs "php": "7.3.x" added, for Heroku at least, otherwise latest would be installed.

Glad you found this useful @zaidaldabbagh - long time no see :D