Advanced search in WordPress themes

For some time now, I’ve been meaning to build an advanced search in WordPress. So now that all the functionality is available in core functions like query_posts, it looks like it’s just a matter of piecing it all together. Easy, right? Previously, I had been using plugins like Multiple Category Selection Widget and Query Multiple Taxonomies, but I either found bugs with new 3.0 features or the widget-style operation too restricting for my purposes. I like widgets, but I wanted my advanced search to appear on its own page.

So here is a quick run through of how you can add an advanced search page to your WordPress theme. For simplicity sake this tutorial will demonstrate how to use multiple categories at once. Truly advanced search would also combine keywords, sorting, filtering and more advanced user input. We’ll save those options for a later day.

Create a page template file in your theme

I really like using page template files, it makes it easier to work in ‘the loop’ and you have more space to build interfaces. In your theme folder create a file called template-advanced-search.php. A WordPress template file only needs the following code to make itself available to pages in wp-admin.

<?php
/*
Template Name: Advanced Search
*/
?>

Create a new page and attach the template file

Now you just need to attach the page template to a new page in wp-admin. Create a new page called ‘Advanced search’. If you created the page correctly you’ll see a reference to it in the page options. Select your template and publish the page.

Page Template Animation

Build form with wp_dropdown_categories

wp_dropdown_categories is a very useful core function that we can quickly use to build our advanced search form. In this example, we’ll be using this function combined with parent and child category groups. Creating parent and child category groups is easy. Go play around in the admin section (wp-admin/edit-tags.php?taxonomy=category) and work it out. Essentially, you want to create the following structure:

• Category 1
  • Child 1
  • Child 2
  • Child 3

Create 3 separate parent child groups.

Here is an example of the code should look now in template-advanced-search.php.

<?php
/*
Template Name: Advanced Search
*/
?>
<h2><a href="<?php the_permalink(); ?>" title="<?php the_title(); ?>"><?php the_title(); ?></a></h2>
<form action="<?php bloginfo('url'); ?>" method="get">
<h3>Category 1</h3>
<div><?php wp_dropdown_categories('child_of=1&show_option_none=Not selected...&hide_empty=1&name=cat[one]'); ?></div>
<h3>Category 2</h3>
<div><?php wp_dropdown_categories('child_of=2&show_option_none=Not selected...&hide_empty=1&name=cat[two]'); ?></div>
<h3>Category 3</h3>
<div><?php wp_dropdown_categories('child_of=3&show_option_none=Not selected...&hide_empty=1&name=cat[three]'); ?></div>
<br />
<div><input class="button" type="submit" name="submit" value="Advanced Search" /></div>
</form>

Now to get the above example to work properly with your categories, you need to edit the code above so that each of the <code>child_of=X</code> references actually refer to real parent category IDs from your WordPress install. So, change the numbers 1, 2 and 3 to the parent category IDs you are using.

Control results with query_post in index.php

Now you just need some code to catch the get parameters from the URL and send that to the query_post function. query_posts will modify the loop to only show the posts that match you’re combination of categories. The following is very simplified code for index.php. If you’re testing this on an existing theme back-up your existing index.php before over-writing.

<?php
if ($_GET['submit'] == 'Advanced Search') {
	$pladvsearchcatids = Array ();
	$pladvsearchcatnames = Array ();
	foreach ($_GET['cat'] as &$pladvsearchcatvalue) {
		if ( $pladvsearchcatvalue != "-1" ) {
			array_push($pladvsearchcatids, $pladvsearchcatvalue);
		}
	}
}
global $wp_query;
query_posts( array_merge( $wp_query->query, array( 'category__and' => $pladvsearchcatids )));
if (have_posts()) :
   while (have_posts()) :
      the_post();
      the_content();
   endwhile;
endif;
?>

That’s it, now you should have the basics of advanced multi-category search working.

If you have any questions, please use the comments below…

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