Two people visit our site one day and they both upload videos about Vitamin C. One person decides to tag his video with ‘Vitamin C’ while the other goes for ‘Ascorbic Acid’. Normally if someone searches our site for one of the terms he would only get the appropriate video. By injecting some MeSH magic we know that Vitamin C is the same thing as Ascorbic Acid so we can serve both results when searching for either term.

There are some more obscure (for me) term equivalencies like ‘Calcymycin’ which is the same as ‘A-23187′. The other great feature of MeSH is that it tries to be as complete as can be. In the example above MeSH also has ‘A 23187′, ‘A23187′ and for ‘Somatostatin receptors’ it contains variations like ‘Receptors, somatostatin’. By storing these directly in our database there is no need to do any advanced matching which would eat up some resources considering the 177,000-ish entries.

The MeSH website contains a lot of information about why and how they work. You can also grab the database in various formats. Since I needed an SQL database I parsed the XML file and compiled the results into two tables. The data_mesh_term table contains the MeSH headings which are the ‘official’ main terms. The data_mesh_term_synonym table contains all the variations for the terms. Feel free to download the zip file which contains the data in an sql file.

Downloads

• Download the SQL database (1.3MB, 19.8 uncompressed)

The paginate_links() function allows you to create very easily customizable pagination which you can use completely out of the loop as well.

$list = new WP_Query($query_args);
$pagination = array(
	'base'       => str_replace( 99999, '%#%', get_pagenum_link( 99999 ) ),
	'format'     => '?paged=%#%',
	'current'    => max( 1, get_query_var( 'paged' ) ),
	'total'      => $list->max_num_pages,
	'next_text'  => 'next',
	'prev_text'  => 'previous'
);
echo '<div class="pagination primary-links">' . paginate_links( $pagination ) . '</div>';

Since the function does not use the loop directly you can use it for listing anything as long as you know the current page and the total number of pages.

$list = range(1, 200);
$items_per_page = 12;
$pagination = array(
	'base'       => get_bloginfo( 'url' ) . '/mypage/%_%',
	'format'     => '?paged=%#%',
	'current'    => $_GET['current_page'],
	'total'      => ceil( max($list) / $items_per_page ),
	'next_text'  => 'go forth',
	'prev_text'  => 'go back'
);
echo '<div class="pagination primary-links">' . paginate_links( $pagination ) . '</div>';

Sending you home with a note

if ( $result ) {
    echo 'Your display named has been changed to ' . $result['display_name'];
}

So what’s the problem here? The above will throw a notice if $result is not defined. If notices are not shown this works as intended but is still sloppy. The reason it works is that when a variable is not set it evaluates to false. Hence the statement is echoed above if $result is set otherwise nothing happens.

Empty Inside

Similarly as above an unset variable is not the same as an empty variable so the below code will also throw a notice since we are trying to see if an unset variable is empty.

if ( empty( $result ) ) {
    echo 'Your display named could not be changed';
}

The proper way to do this

if ( isset( $result ) AND !empty( $result ) ) {
    echo 'Your display named has been changed to ' . $result['display_name'];
}

When Sloppiness Leads To Bugs

Say you’re creating a WordPress theme and you want the user to be able to specify a logo. If no logo is specified the site title is shown in heading text.

$logo = get_option( 'my_site_logo' );
if ( isset( $logo ) ) {
    echo '';
}
else {
    echo '
' . get_bloginfo() . '

';
}

So let’s see what a user would do/see. He downloads the theme, activates it and sees his new website with the website title in a nice heading on top. He then decides to use a logo instad so pastes the URL of an image he uploaded. The image shows up, the user is awesome happy and all is well.

Once day he decides to switch back to the text again until all is well so he removes the URL from the input box. He goes back to his where there is now no logo and no title either. He is furious and eats his own arm in sorrow.

In this case the ‘my_site_logo’ option is still in the database, it just has an empty value. So when you pull it $logo will be set as if you would have hard coded it like so: $logo = ''. When we get to the if statement $logo is set so the image is output but the source will be empty.

To prevent this you should always use isset() and empty() in conjunction.

$logo = get_option( 'my_site_logo' );
if ( isset( $logo ) AND !empty( $logo ) ) {
    echo '';
}
else {
    echo '
' . get_bloginfo() . '

';
}

Don’t Trust Yourself

Many programmers’ first reaction is that this is stupid. When saving the option we always check to make sure the value isn’t empty. If it is we delete the option from the database which means that the emptiness check isn’t necessary.

While this is true this is just bad practice and you are opening yourself up to bugs. Even with the best coding practices we get so many bugs it’s a shame to have to spend time fixing ones we cluld have prevented easily.