User gets logged out, after post upload [PHP] - php

Question

I got a problem with my post upload formula and need your help.
With this formula, I inserted data into 2 tables at same time and it worked perfectly fine. My next step was to insert the userid in the post table, so that the post is linked to the creator of the post.
Inserting the userid in the post table worked as well but after the upload, the user gets logged out.
Here is a part of my code
(I marked the code where I think there is something wrong with a "X")
session_start();
$db = mysqli_connect("localhost", "root", "", "abc");
if (isset($_POST['upload_post']))
{
$ad_post_title = mysqli_real_escape_string($db, $_POST['post_title']);
X $user_id = $_SESSION['id_u'];
X $_SESSION['id_u'] = mysqli_insert_id($db);
X $sql_p = "INSERT INTO ad_posts (post_title, user_id) VALUES ('$post_title','$user_id')";
if (mysqli_query($db, $sql_p))
{
$ad_post_id = mysqli_insert_id($db);
...
}
}
Maybe I have done something wrong with the session?

Answer 1

On the second line of your code you are overwriting a session variable of the users id, which I figure you're using to make sure the user is logged in, with the id of the newly inserted row.
$user_id = $_SESSION['id_u'];
X $_SESSION['id_u'] = mysqli_insert_id($db);
$sql_p = "INSERT INTO ad_posts (post_title, user_id) VALUES ('$post_title','$user_id')";
In the code you supplied I do not see are reason for this second line, remove it and your user won't be logged out, unless of course you're overwriting it somewhere else also.

Answer 2

You cannoT use mysqli_insert_id() before add data in the system.
I checked same code in my system and its working fine.
session_start();
$db = mysqli_connect("localhost", "root", "", "abc");
if (isset($_POST['upload_post']))
{
$ad_post_title = mysqli_real_escape_string($db, $_POST['post_title']);
$user_id = $_SESSION['id_u'];
$sql_p = "INSERT INTO ad_posts (post_title, user_id) VALUES ('$post_title','$user_id')";
if (mysqli_query($db, $sql_p))
{
$ad_post_id = mysqli_insert_id($db);
...
}
}