When trying to change username MySQL Query Fails - php

Question

I have some users in the database and I can edit their names and passwords but when I try to edit the username the query fails.
Here is my code
$user->username = $db->mysql_prep($_POST["username"]);
$user->hashed_password = ($_POST["password"]);
$user->firstname = $db->mysql_prep($_POST["firstname"]);
$user->lastname = $db->mysql_prep($_POST["lastname"]);
$user_query = $user->find_user_by_username($user->username);
$user->id = $user_query["id"];
$result = $user->change_user_by_id($user);
//->id,$user->username,$user->hashed_password,$user->firstname,$user->lastname
unset($user);
My change_user_by_id method:
public function change_user_by_id($user){
global $db;
global $session;
$query = "UPDATE users SET ";
$query .= "username = '{$user->username}', ";
$query .= "first_name = '{$user->firstname}', ";
$query .= "last_name = '{$user->lastname}' ";
$query .= "WHERE id = {$user->id} ";
$query .= "LIMIT 1";
$result = mysqli_query($db->connection, $query);
$db->confirm_query($result);
if ($result && mysqli_affected_rows($db->connection) == 1) {
// Success
$session->message("User updated.");
redirect_to("list.php");
} else {
// Failure
$session->message("User update failed.");
}
}
And my find_user_by_username method:
public static function find_user_by_username($username="default"){
global $db;
$query = "SELECT * ";
$query .= "FROM users ";
$query .= "WHERE username = '{$username}' ";
$query .= "LIMIT 1";
$user_set = mysqli_query($db->connection, $query);
$db->confirm_query($user_set);
if($user = mysqli_fetch_assoc($user_set)) {
return $user;
} else {
return null;
}
}
EDIT:
The only error I get is from confirm_query function I get the message "Database query failed" Here is the function:
public function confirm_query($result_set) {
if (!$result_set) {
die("Database query failed.");
}
}
EDIT 2:
Added error messages and this is what I get:
You have an error in your SQL syntax; check the manual that
corresponds to your MySQL server version for the right syntax to use
near 'LIMIT 1' at line 1

Answer 1

I figured it out it was caused by using the username to get the id, which means changing the username meant no id could be retrieved. So I changed my code and added a hidden field for id in my form.
Old code:
$user->username = $db->mysql_prep($_POST["username"]);
$user->hashed_password = ($_POST["password"]);
$user->firstname = $db->mysql_prep($_POST["firstname"]);
$user->lastname = $db->mysql_prep($_POST["lastname"]);
$user_query = $user->find_user_by_username($user->username);
$user->id = $user_query["id"];
$result = $user->change_user_by_id($user);
unset($user);
replaced by new code:
$user->username = $db->mysql_prep($_POST["username"]);
$user->hashed_password = ($_POST["password"]);
$user->first_name = $db->mysql_prep($_POST["first_name"]);
$user->last_name = $db->mysql_prep($_POST["last_name"]);
$user->id = $db->mysql_prep($_POST["id"]);
$result = $user->change_user_by_id($user);
unset($user);