Some misunderstanding with pagination - php

Question

I am trying to make pagination from one post to the next post in a single blog post. The problem is that when I open an article with ID-1 and I click on the 'next' button I get a blank/empty page.
This is the post page, which gets the ID of the chosen post in blog.php. This is what I have so far. Any suggestions?
<?php
// include database connection
require_once 'database.inc.php';
$pdo = Database::connect();
if(isset($_GET['post_id']) && is_numeric($_GET['post_id'])){
$post_id = $_GET['post_id'];
// page is the current page, if there's nothing set, default is page 1
$page = isset($_GET['page']) ? $_GET['page'] : 1;
// set records or rows of data per page
$recordsPerPage = 1;
// calculate for the query LIMIT clause
$fromRecordNum = ($recordsPerPage * $page) - $recordsPerPage;
// select all data
$query = "SELECT * FROM posts WHERE post_id = $post_id LIMIT {$fromRecordNum}, {$recordsPerPage}";
$stmt = $pdo->prepare( $query );
$stmt->execute();
//this is how to get number of rows returned
$num = $stmt->rowCount();
//check if more than 0 record found
if($num>0){
while ($row = $stmt->fetch(PDO::FETCH_ASSOC)){
echo '
// post body ';
}
}
// *************** <PAGING_SECTION> ***************
// ***** for 'first' and 'previous' pages
if($page>1){
// ********** show the previous page
$prev_page = $page - 1;
echo "
<a href='" . $_SERVER['PHP_SELF'] . "?page={$prev_page}'>
<div class='prev-btn control-nav text-left'>
<h5>Previous Post</h5>
</div>
</a>";
}
// find out total pages
$query = "SELECT COUNT(*) as total_rows FROM posts";
$stmt = $pdo->prepare( $query );
$stmt->execute();
$row = $stmt->fetch(PDO::FETCH_ASSOC);
$total_rows = $row['total_rows'];
$total_pages = ceil($total_rows / $recordsPerPage);
if($page<$total_pages){
// ********** show the next page
$next_page = $page + 1;
echo "<a href='" . $_SERVER['PHP_SELF'] . "?page={$next_page}'>
<div class='next-btn control-nav text-right'>
<h5>Next Post</h5>
</div>
</a>";
}
}
?>

Answer 1

It's not very clear from your question, but I think your problem is this, your code requires the post_id parameter to be set:
if(isset($_GET['post_id']) && is_numeric($_GET['post_id'])){
$post_id = $_GET['post_id'];
}
But in your next and prev page links, you're not setting a post_id parameter:
echo "<a href='" . $_SERVER['PHP_SELF'] . "?page={$next_page}'>
<div class='next-btn control-nav text-right'>
<h5>Next Post</h5>
</div>
</a>";
Your code is inherently relying on a single post being shown, as determined by the post_id. Here's what I suggest, change:
// select all data
$query = "SELECT * FROM posts WHERE post_id = $post_id LIMIT {$fromRecordNum}, {$recordsPerPage}";
to:
// select all data
$query = "SELECT * FROM posts LIMIT {$fromRecordNum}, {$recordsPerPage}";
of course, then, you won't be able to show a specific post, but then again it's hard to know what you're actually trying to achieve here.

Answer 2

Could you show it in a working website? It would be easier to tell what is wrong then, but from the code it looks like you are making the url wrong in your anchor href part.
$prev_page = $post_id - 1;
<a href='" . $_SERVER['PHP_SELF'] . "?post_id={$prev_page}'>
<div class='prev-btn control-nav text-left'>
<h5>Previous Post</h5>
</div>
</a>"
$next_page = $post_id + 1;
and the link is there made in same manner as previous one
as i am not sure what your server php self is returning and you shouldnt be adding the second ? symbol in it, if it already had it and u should use & i think for get parameters as ? is only used once after the script file name once. Or you are either missing the ID in your url.
Also blank/empty page might be crashing the script on that page and if u have errors turned off you wont see it in webpage and will have to go to your php errors log file to look for them
EDIT: as block quote wasnt showing correctly.

Answer 3

It is because first you get $post_id but then in the links you put $page which doesn't contain your ID. Try to change your nex&prev links like this:
<a href='" . $_SERVER['PHP_SELF'] . "?post_id=".$prev_page."'>
<a href='" . $_SERVER['PHP_SELF'] . "?post_id=".$next_page."'>
Also don't forget to change the line for $page here:
$page = isset($_GET['page']) ? $_GET['page'] : 1;
to this
$page = isset($_GET['post_id']) ? $_GET['post_id'] : 1;
This should do the trick.