在php中连接到数据库并包含一次，但连接文件不在root中

I've created a connect file, which is stored in the folder above the wwwroot for security reasons.

   $con = mysqli_connect("localhost","USERNAME","PASSWORD","DBNAME");

I want to include that only once in header.php so that it can be used globally across all files. I've tried:

   include(dirname(__FILE__) . '/../../connect.php')

However I am having to include the connect.php file in every single file because otherwise it says that my $con object is not an object. I don't know if this has something to do with variable scopes - but if I'm including the header.php in every other file, shouldn't it be available? I keep getting this error:

Fatal error: Call to a member function query() on a non-object

If anyone knows why it would be greatly appreciated!

EDIT: Prefixing $con with global didnt fix it. The only other code that should affect it is:

  <?php include 'includes/header.php'; ?>

And im trying to use it in:

         class CommentFunctions{
    //include_once(dirname(__FILE__) . '/../../connect.php');

    public static function getUserData($userId){

        $result = $con->query("SELECT name,image
                        FROM USERS where userID =  ".$userId);
        if($result){        
            if(mysqli_num_rows($result) == 1){
                return mysqli_fetch_array($result);
            }   
        }
        return null;
    }

which itself is in includes/comments.php

Above $con add:

global $con;

If that doesn't help please paste a larger chunk of code.

In your updated code you have a scope issue. Add global $con inside the method and problem solved.

global $con;
$result = $con->query("SELECT name,image