Elgg\Database::assertInstalled PHP Method

    public function assertInstalled()
    {
        if ($this->installed) {
            return;
        }
        try {
            $sql = "SELECT value FROM {$this->table_prefix}config WHERE name = 'installed'";
            $this->getConnection('read')->query($sql);
        } catch (\DatabaseException $e) {
            throw new \InstallationException("Unable to handle this request. This site is not configured or the database is down.");
        }
        $this->installed = true;
    }