February, 2009 | Digital Wealth

Hiding WordPress categories

When I wrote my first WordPress related post, I admitted that I was only doing it to attract traffic and it would be my last post on the subject. However, I start again. This time around, however, I want to talk about something which isn’t common knowledge and neither did I get any responses on the official WordPress forum regarding this.

Suppose you do not want some of your posts to appear anywhere: not the homepage, not the RSS feeds, not the archives: nowhere. However you DO want it to appear only when its linked to, as a single post on the page. I regularly need to do this, because some part of the post is more like an ‘addendum’ or when including everything would make the post too long.

There is a standard solution available on the forums: creating a plugin and adding code to this effect:

function hs_cat_exclude($query) { if ($query->is_feed || $query->is_home || $query->is_archive ) { $hsq = $query->gt;get('cat'); if (!isset($hsq)) { $hsq = '-22'; } else { $hsq = $hsq . ",-22"; } $query->gt;set('cat',$hsq); } return $query; }

add_filter('pre_get_posts','hs_cat_exclude');

Here, 22 is the category number of the category I wanted to exclude.

This code works fine, but the moment you add is_category to the ‘if‘ clause, it doesn’t work for the category page. This was perplexing to me, and I did not understand it. I spent a long time and then decided to dig deeper. I found out that the ‘wiring’ is faulty (this is what I believe). It can’t work like this for the category page. What is needed additionally is something like this:

function hs_cat_exclude_cat($where) { global $wp_query; if ($wp_query->is_category) { $where = $where . " AND NOT EXISTS(SELECT 1 FROM wp_term_relationships WHERE wp_term_relationships.object_id=wp_posts.id AND wp_term_relationships.term_taxonomy_id='22')"; } return $where; }

add_filter(‘posts_where’,’hs_cat_exclude_cat’);

So far so good. What I wanted over and above this though, is for the category to not even appear on the category widget. I tried to find a way to get this done through the plugin but it did not work. Ultimately I had to ‘hack’ one of the core files to achieve this. If anyone knows of a better way to accomplish this, please add a comment. The change is to wp-includes/widgets.php. Find the line of code that looks like:

$cat_args = array('orderby' => 'name', 'show_count' => $c, 'hierarchical' => $h);

added an ‘exclude’ clause like this:

$cat_args = array('orderby' => 'name', 'show_count' => $c, 'hierarchical' => $h, 'exclude' => 22);

Thats all there is to it.

Update Jan 12th 2010: Since WP 2.8 I believe (I noticed the problem in 2.9.1), the last change above needs to be done to default-widgets.php rather than widgets.php

Remembering your passwords

In today’s online world we have to remember a lot of passwords. Security advice is that they must all be different (so that if one account is compromised, we don’t loose the security of all accounts), and be changed every now and then.

It is sometimes difficult to cope with such requirements, without writing down the passwords – and if you do write them down, what happens if you loose your notebook?

The answer to such problems is a piece of software called ‘Password Safe’ – it has been developed under the watchful eyes of a well known security expert. It keeps all your passwords encrypted by one single password. So you only need to remember one password from now on. You can keep the software on a USB pen-drive (its even platform independent so you can run it both on Windows and Linux) and take it along with you – no harm if you loose the pen-drive – no one can retrieve your passwords.

Note that there are a lot of different software applications with the same name, and not all of them may be equally secure. Please download only from http://passwordsafe.sourceforge.net/.

Note: this is not professional advise, use at your own risk.

Generating sequential numbers in a database

You are creating an application that allows organisations to manage employees. One of the tasks that it has to do is generate an employee ID when a new employee is being entered. One way of doing this is through this query:

SELECT max(empl_id)+1 FROM employee;

However, this query presents a problem in a multiuser environment: if more than one user is entering employee details at the same time, they will both get the same empl_id. To tide over this problem, one way to go is to look at the auto numbering solution provided by the database – however I personally find that solution limiting and have never used it.

The other approach is to create a single row table for global settings (in all probability your application will already have this) and maintain a field in that table as the last number used. Thereafter, the code can be written as below:
UPDATE settings_tbl SET lastnumber=lastnumber+1;

SELECT lastnumber FROM settings_tbl;

Remember that the order of the queries is important in a multiuser environment. Placing SELECT before the UPDATE can cause problems (locking has to happen first).

This piece of code should be executed at the time of saving the employee and not when a request for the blank employee form is generated. This is necessary so that one user of the application doesn’t have to wait for another to be finished. Note that the UPDATE lock is released only when you do the COMMIT or ROLLBACK.

Another way of doing the same thing in Oracle, one that I prefer myself and have used in a number of tight situations is the FOR UPDATE clause. This one allows you to do the SELECT first:
SELECT lastnumber FROM settings_tbl FOR UPDATE;

UPDATE settings_tbl SET lastnumber=lastnumber+1;