Connection Error:SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo for localhost.dbname=myblog failed: No such host is known

This is my code:

<?php
class Database {

    private $host = 'localhost';
    private $db_name = 'myblog';
    private $username = 'root';
    private $password = '';
    private $conn;


public function connect() {
    $this->conn = null;

    try {
        $this->conn = new PDO('mysql:host=' . $this->host . '.dbname=' . $this->db_name,
         $this->username, $this->password);
        $this->conn->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
    } catch(PDOException $e) {
        echo 'Connection Error:' .$e->getMessage();
    }
    return $this->conn;
}
}

And this what did they say

Connection Error:SQLSTATE[HY000] [2002] php_network_getaddresses: getaddrinfo for localhost.dbname=myblog failed: No such host is known. <br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function prepare() on null in C:UsersagadirDownloadsxampp3htdocsAPI projectModelspost.php:38
Stack trace:
#0 C:UsersagadirDownloadsxampp3htdocsAPI projectAPIPOSTread.php(18): Post-&gt;read()
#1 {main}
  thrown in <b>C:UsersagadirDownloadsxampp3htdocsAPI projectModelspost.php</b> on line <b>38</b><br />