Previous/next button in PHP - php

Question

I´m pretty much entirely new to PHP, so please bear with me.
I´m trying to build a website running on a cms called Core. I'm trying to make it so that the previous/next buttons cycle through tags rather than entries. Tags are stored in a database as core_tags. Each tag has it own tag_id, which is a number. I've tried changing the excisting code for thep previous/next buttons, but it keeps giving me 'Warning: mysql_fetch_array() expects parameter 1 to be resource, null given in /home/core/functions/get_entry.php on line 50'.'
Any help would be greatly appreciated.
Get_entry.php:
<?php
$b = $_SERVER['REQUEST_URI'];
if($entry) {
$b = substr($b,0,strrpos($b,"/")) . "/core/";
$id = $entry;
$isPerma = true;
} else {
$b = substr($b,0,mb_strrpos($b,"/core/")+6);
$id = $_REQUEST["id"];
}
$root = $_SERVER['DOCUMENT_ROOT'] . $b;
$http = "http://" . $_SERVER['HTTP_HOST'] . substr($b,0,strlen($b)-5);
require_once($root . "user/configuration.php");
require_once($root . "themes/".$theme."/configuration.php");
require_once($root . "functions/session.php");
if(is_numeric($id)) {
$type = "entry";
} else {
$type = "page";
}
$id = secure($id);
if($type == "page") {
$data = mysql_query("SELECT p.* FROM core_pages p WHERE p.page_title = \"$id\"");
$page_clicks = 0;
while($p = mysql_fetch_array($data)) {
$url = $p["page_url"];
$path = $root . "user/pages/" . $url;
$page_clicks = $p['hits']+1;
require($path);
}
mysql_query("UPDATE core_pages p SET
p.hits = $page_clicks
WHERE p.page_title = $id");
}
if($type == "entry") {
// queries the dbase
$data_tags = mysql_query("SELECT entry_id,entry_title FROM core_entries WHERE entry_show = 1 ORDER BY entry_position DESC") or die(mysql_error());
$navArr=array();
while($tmparray = mysql_fetch_array($data_entries,MYSQL_ASSOC)){
array_push($navArr,$tmparray['entry_id']);
}
function array_next_previous($array, $value) {
$index = array_search($value,$array);
//if user clicked to view the very first entry
if($value == reset($array)){
$return['prev'] = end($array);
$return['next'] = $array[$index + 1];
//if user clicked to view the very last entry
}else if($value == end($array)){
$return['prev'] = $array[$index - 1];
reset($array);
$return['next'] = current($array);
}else{
$return['next'] = $array[$index + 1];
$return['prev'] = $array[$index - 1];
}
return $return;
}
$data = mysql_query("SELECT e.* FROM core_entries e WHERE e.entry_id = $id AND e.entry_show = 1");
$entry_clicks = 0;
if(#mysql_num_rows($data) < 1) {
die("Invalid id, no entry to be shown");
}
while($e = mysql_fetch_array($data)) {
$nextPrevProject = array_next_previous($navArr,$id);
$entry_id = $e['entry_id'];
$entry_title = $e['entry_title'];
// DATE
$t = $e["entry_date"];
$y = substr($t,0,4);
$m = substr($t,5,2);
$d = substr($t,8,2);
$entry_date = date($date_format,mktime(0,0,0,$m,$d,$y));
$entry_text = $e['entry_text'];
$entry_extra1 = $e['entry_extra1'];
$entry_extra2 = $e['entry_extra2'];
$entry_client = $e['entry_client'];
$entry_position = $e['entry_position'];
$entry_hits = $e['hits']+1;
$entry_new = $e['entry_new'];
if($entry_new == 1) {
$isNew = true;
} else {
$isNew = false;
}
if($nice_permalinks) {
$entry_perma = "$http".$entry_id;
} else {
$entry_perma = "$http"."?entry=$entry_id";
}
$data_e2t = #mysql_query("SELECT e2t.tag_id FROM core_entry2tag e2t WHERE e2t.entry_id = $entry_id");
$tag_str = "";
while($e2t = #mysql_fetch_array($data_e2t)) {
$tag_id = $e2t["tag_id"];
$data_tags = #mysql_query("SELECT t.tag_text FROM core_tags t WHERE t.tag_id = $tag_id");
while($t = #mysql_fetch_array($data_tags)) {
$tag_text = $t["tag_text"];
$tag_str = $tag_str . "<a class=\"tag-link\" name=\"tag".$tag_id."\" href=\"#tag-"._encode($tag_text)."\">".$tag_text."</a>".$separator_tags;
}
}
$entry_tags = substr($tag_str,0,strlen($tag_str)-strlen($separator_tags));
$layout_path = $root . "user/uploads/" . treat_string($entry_title) . "/layout.php";
if(is_file($layout_path) && (#filesize($layout_path) > 0)) {
require($layout_path);
} else {
require($theme_path . "parts/entry.php");
}
}
mysql_query("UPDATE core_entries e SET
e.hits = $entry_hits
WHERE e.entry_id = $id");
}
if($isPerma) {
echo "<a class=\"index-link\" href=\"$http\">back to index</a>";
}
?>

Answer 1

You have not defined $data_entries, before using it here:
while($tmparray = mysql_fetch_array($data_entries,MYSQL_ASSOC)){
array_push($navArr,$tmparray['entry_id']);
}
That is why you get the very descriptive error message.
Did you mean to use $data_tags?

Answer 2

Use: "SELECT p.* FROM core_pages p WHERE p.page_title = '".$id."'
Note: mysql_connect is not sql-injection save. If you use mysql_connect, change to PDO.

Answer 3

$data_entries is not defined on line 50, then mysql_fetch_array return an exception of null value given.
Try to change $tmparray = mysql_fetch_array($data_entries,MYSQL_ASSOC) to $tmparray = mysql_fetch_array($data_tags,MYSQL_ASSOC).
Hope this help!