Php call to member function query() on a non-object error - php

Question

I'm using mysqli for a function, and I'm getting an error, Fatal error: Call to a member function query() on a non-object in /home/u250000297/public_html/forum/system/db.php on line 46 I've tried different things, but I just get different errors, what am I doing wrong and where is my error?
Code lines 45-51:
function fetch($query) {
$sql = $mysqli->query($query);
$result = $sql->fetch_array(MYSQLI_BOTH);
return $result;
$sql->free();
}
Here's my previous attempt and error : Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /home/u250000297/public_html/forum/system/db.php on line 46 Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in /home/u250000297/public_html/forum/system/db.php on line 47 Warning: mysqli_query() expects parameter 1 to be mysqli, null given in /home/u250000297/public_html/forum/system/db.php on line 46 Warning: mysqli_fetch_array() expects parameter 1 to be mysqli_result, null given in /home/u250000297/public_html/forum/system/db.php on line 47
Code, lines 45-51:
function fetch($query) {
$sql = mysqli_query($mysqli, $query);
$row = mysqli_fetch_array($sql, MYSQLI_BOTH);
return $row;
mysqli_free_result($row);
}
Connection:
$mysqli = mysqli_connect($this->host,$this->username,$this->password);
mysqli_select_db( $mysqli,$this->database );
if ($mysqli->connect_error) {
trigger_error('Database connection failed: ' . $mysqli->connect_error, E_USER_ERROR);
}

Answer 1

Either you need to define $mysqli as global or pass it as an argument.
After a return, no statement will be executed (mysqli_free).
Global:
function fetch($query) {
global $mysqli;
$sql = $mysqli->query($query);
$result = $sql->fetch_array(MYSQLI_BOTH);
return $result;
}
Parameter (and even better):
function fetch($myslqi, $query) {
$sql = $mysqli->query($query);
$result = $sql->fetch_array(MYSQLI_BOTH);
return $result;
}

Answer 2

Points to debug are
1) Is the connection to the database getting established?
2) Are your query strings correct?
Call to a member function query() on a non-object and Warning: mysqli_query() expects parameter 1 to be mysqli means that the $mysqli is null or isn't initialized properly. To get more information check the mysql error logs.