HTML/PHP Syntax to Move to Next Record Button - php

Question

I am developing on an HTML page a "go to next record" button.
Well, it goes to the next record once and then stops. Nothing happens when clicking on the "Prior Issue" button after the initial click. Since I increment the issue number, the cursor should move to the next record. I am only working on the "Prior Issue" button currently.
HTML syntax:
<a href="index.php?content=main_window&id=1" title="Show More Recent Issue" >< Next (Newer) Issue</a> &nbsp &nbsp &nbsp &nbsp &nbsp &nbsp <a href="index.php?main_window&id=-1 title ="Show Older Issue" >Prior (Older)) Issue ></a>
The variable "id" is past to:
// Get Cycle Direction "1" stands for newer issue, "0" No Direction set, "-1" stands for older issue
if (!isset($_REQUEST['id']))
{$cycle_direction=0;
} else {
$cycle_direction = trim($_REQUEST['id']);
}
Which then gets past to: (only working on the "case -1" at this time.
switch(trim($cycle_direction))
{
case -1:
// display an older issue
echo "Decrement<br>";
$current_record_number=$current_record_number +1;
echo $current_record_number;
mysqli_data_seek($result, 0);
mysqli_data_seek($result, $current_record_number);
$row=mysqli_fetch_row($result);
printf ("%s \n",$row[0]);
$issuenum=$row[0];
break;
case 0:
// display current issue
//echo "No Selection";
break;
case 1:
// display newer issue
//echo "Increase";
$issuenum=2165;
break;
}

Answer 1

Do it right way. All what you need is url with next/prev record's ids.
$current_id = isset($_GET['id']) ? intval($_GET['id']) : 0;
// in case you are using MySQL
$query = "SELECT
prev_id, next_id
FROM
(SELECT
id AS prev_id
FROM
issues
WHERE
id < $current_id
LIMIT 1) a,
(SELECT
id AS next_id
FROM
issues
WHERE
id > $current_id
LIMIT 1) b";
// fetch query data
$prev_id = ...
$next_id = ...
// SHOW CURRENT ISSUE
echo '<a href="index.php?content=main_window&id='.$next_id.'" title="Show More Recent Issue" >< Next (Newer) Issue</a> - <a href="index.php?main_window&id=$prev_id title ="Show Older Issue" >Prior (Older)) Issue ></a>';
In case you get your data from any other db, the logic is the same. Just select previous and next ids, and provide urls using $prev_id and $next_id.
Another solution using MAX/MIN trick.
$query = "SELECT
(SELECT MAX(id) FROM issues WHERE id < t.id) as prev_id,
(SELECT MIN(id) FROM issues WHERE id > t.id) as next_id
FROM issues t WHERE t.id = $current_id";

Answer 2

"Beta" version now working. I stripped the code down to the very bare essentials and added many echo statements to observe how the program responded. The short answer, PHP does not have a memory between each web-page so the values of the variables are "lost". While I was dimly aware of this, it did not become obvious for a while.
The solution was to develop a several $_SESSION variables to hold the array and to monitor the location of the cursor.
<?php
// Start the session
session_start();
include ("establish_array.php");
?>
The code below constitutes "establish_array.php" to establish the array in: "$_SESSION['result']".
<?php
require_once 'php_data/login_data.php';
$conn = new mysqli($hn, $un, $pw, $db);
if ($conn->connect_error) die($conn->connect_error.' Sorry, could not connect to the sfmags database server');
$query = "Select IssueIDNUM FROM tblIssueList ORDER by IssueDate DESC, IssueIDNUM ";
$_SESSION['result'] =$conn->query($query);
if (!$_SESSION['result']) die($conn->error);
$_SESSION['rowcount'] = mysqli_num_rows($_SESSION['result']);
?>
The code below is embedded in a case (switch) statement to move the magazine issue to the next older magazine when the pseudo "next" HTML key is pressed. The function "return_row_number();" returns the current row number, +1 is added to the row number and "mysqli_data_seek" is used to move to the next (older) record (issue).
$issuenum = $_SESSION['issuenum'];
$_SESSION['cursor_location'] = return_row_number();
echo "Cursor Location :" . $_SESSION['cursor_location'] . "<br>";
$_SESSION['cursor_location'] = $_SESSION['cursor_location'] + 1;
mysqli_data_seek($result, 0);
mysqli_data_seek($result,$_SESSION['cursor_location']);
$row=mysqli_fetch_row($result);
$issuenum=$row[0];
$_SESSION['issuenum'] = $issuenum;
echo "Issue Number: $issuenum <br>";
Thanks to: misunderstood, Unheiiig, and Alexander Ravikovich for providing useful advice and clues.

Answer 3

Update
This is what I got from your comment:
function return_row_number() {
// Loop through the Array; Get Row Number for the current issue global $result,$issuenum, $rowcount;
$count =0;
mysqli_data_seek($result, 0);
while($row=mysqli_fetch_array($result, MYSQL_ASSOC)) {
++$count;
if($issuenum == $row['IssueIDNUM']) {
return $count -1; break;
}
}
}
Now the mystery value is $issuenum.
And there is a terminology problem. This is not "Looping through an Array" it is querying the database and and looping through the query results.
This is a rather inefficient method of finding the next record. But before correcting that, you need to explain where the value for $issuenum is coming from.
It would also help to know more about the database table especially:
How many issue records?
What is the numbering scheme?
How often does a new issue get added?
end of update
With this line of code you will always get a value of 1
$current_record_number=$current_record_number +1;
because $current_record_number = 0.
You should add the current issue to the href where xx=current record #.
I changed "id" to "cycle"
added content= to Next href.
<a href="index.php?content=main_window&cycle=1&rec=xx"
title="Show More Recent Issue" > < Next (Newer) Issue</a>
&nbsp &nbsp &nbsp &nbsp &nbsp &nbsp
<a href="index.php?content=main_window&cycle=-1&rec=xx
title ="Show Older Issue" >Prior (Older)) Issue ></a>
Then add this to your PHP:
$current_record_number = intval($_GET['rec']);
And change:
$cycle_direction = trim($_REQUEST['id']);
To:
$cycle_direction= intval($_GET['cycle']);
Instead of trim and isset you should just use intval()
$cycle_direction = intval($_REQUEST['id']);
Also instead of $current_record_number=$current_record_number +1;
You could use: $current_record_number += $cycle_direction
and eliminate the switch.
Unconventional approach
Let's say issues have values from 1 to 10.
$next[-1] = array(0,10,1,2,3,4,5,6,7,8,9,1);
$next[1] = array(0,2,3,4,5,6,7,8,9,10,1);
$next[0] = array(0,1,2,3,4,5,6,7,8,9,10);
$nextIssue = $next[intval($_REQUEST['id'])];
If issues are numbered 2001 to 2010
$nextIssue = 2000 + $next[intval($_REQUEST['id'])];
No matter how many issues you have there is no need to use a database.
Create the $next array as shown above, then save the array.
$fp = fopen('next.ser','w');
fwrite($fp,serialize($next));
fclose($fp);
When you need the $next array in an app use:
$next= unserialize(file_get_contents('next.ser'));