Error making a php PDO query with postgresql

Good I am trying to make a web service with php and postgresql as a database, but I want to do it by the PDO method and I get errors.

<?php
require "database.class.php";
class Users
{

 private $con;
 public function __construct()
 {

 //en $this->con tenemos la conexión con la bd pruebas
 $this->con = new Database();

 }

 //obtenemos usuarios de una tabla con postgreSql
 public function getUsers()
 {

     try{

     $query = $this->con->prepare('SELECT * FROM res_partner');
     $query->execute();
     $this->con->close_con();
     return $query->fetchAll();

     } catch(PDOException $e) {

             echo  $e->getMessage(); 

         }

 }

 Users::getUsers();

}

The connection is established here

<?php
$host='------';
$db = 'DiiNLAB';
$username = 'odoo';
$password = '--';