I knew that this should be relatively easy to accomplish. WordPress 3.1 extended the way that taxonomies can be queried which allows for a great deal of fine tuning. Read more about Advanced Taxonomy Queries in WordPress.

So, without further ado, here’s the solution … as well as a couple of things I learned along the way.

5 Most Recent Posts – No Links

Passing the tax_query argument to get_posts(). The following configuration allows you to exclude all posts having the “Link” post format.

$no_links = get_posts( array(
	'tax_query' => array(
		array(
		  'taxonomy' => 'post_format',
		  'field'    => 'slug',
		  'terms'    => array( 'post-format-link' ),
		  'operator' => 'NOT IN'
		)
	)
) );

Only Links

By replacing NOT IN with IN for the operator argument, we can easily make the query return only link posts.

$links = get_posts( array(
	'tax_query' => array(
		array(
		  'taxonomy' => 'post_format',
		  'field'    => 'slug',
		  'terms'    => array( 'post-format-link' ),
		  'operator' => 'IN'
		)
	)
) );

More Than Just Links!

If you need to include or exclude posts of another format, you can modify the value of the terms arg with anything from the following list:

• post-format-aside
• post-format-audio
• post-format-chat
• post-format-gallery
• post-format-image
• post-format-link
• post-format-status
• post-format-quote
• post-format-video

Combine a Few Different Post Formats

The terms arg has been designed specifically to enable you to include or exclude more than one term. If you wanted to exclude both links and status updates from your query, the following should do the trick.

$exclude_links_and_status = get_posts( array(
	'tax_query' => array(
		array(
		  'taxonomy' => 'post_format',
		  'field'    => 'slug',
		  'terms'    => array( 'post-format-link', 'post-format-status' ),
		  'operator' => 'NOT IN',
		)
	)
) );

Showing Only Standard Posts

Perhaps you have a blog with posts of many, many different formats (These are good problems to have btw. I only use two ). What do you do if you only want to display a list of regular-old-posts? You’ll probably want to exclude all of the post formats.

Get a List of All Post Formats

$formats = get_post_format_slugs();

Massage the Post Formats

The get_post_format_slugs() function returns the simple, easy to read name for each post format. We will need to use the long-form name of the post format in our query. We’ll just loop over format names and add a bit of info to the beginning of name.

foreach ( (array) $formats as $i => $format ) {
	$formats[$i] = 'post-format-' . $format;
}

Run the Query

All that’s left to do is pass of the the formats as the terms argument and set the operator argument to NOT IN.

$standard_posts = get_posts( array(
	'tax_query' => array(
		array(
		  'taxonomy' => 'post_format',
		  'field'    => 'slug',
		  'terms'    => $formats,
		  'operator' => 'NOT IN'
		)
	)
) );

Here’s all of it together for easy copy-and-paste. I even threw in a simple loop at no extra charge!

$formats = get_post_format_slugs();

foreach ( (array) $formats as $i => $format ) {
	$formats[$i] = 'post-format-' . $format;
}

$standard_posts = get_posts( array(
	'tax_query' => array(
		array(
		  'taxonomy' => 'post_format',
		  'field'    => 'slug',
		  'terms'    => $formats,
		  'operator' => 'NOT IN'
		)
	)
) );

global $post;

foreach( (array) $standard_posts as $post ) {
	setup_postdata( $post );
	print '<div>';
	the_title( '<h2>', '</h2>' );
	the_content();
	print '</div>';
}

wp_reset_postdata();

/**
 * Define default terms for custom taxonomies in WordPress 3.0.1
 *
 * @author    Michael Fields     http://wordpress.mfields.org/
 * @props     John P. Bloch      http://www.johnpbloch.com/
 *
 * @since     2010-09-13
 * @alter     2010-09-14
 *
 * @license   GPLv2
 */
function mfields_set_default_object_terms( $post_id, $post ) {
	if ( 'publish' === $post->post_status ) {
		$defaults = array(
			'post_tag' => array( 'taco', 'banana' ),
			'monkey-faces' => array( 'see-no-evil' ),
			);
		$taxonomies = get_object_taxonomies( $post->post_type );
		foreach ( (array) $taxonomies as $taxonomy ) {
			$terms = wp_get_post_terms( $post_id, $taxonomy );
			if ( empty( $terms ) && array_key_exists( $taxonomy, $defaults ) ) {
				wp_set_object_terms( $post_id, $defaults[$taxonomy], $taxonomy );
			}
		}
	}
}
add_action( 'save_post', 'mfields_set_default_object_terms', 100, 2 );

You will need to configure the $defaults array to reflect your wishes. The keys are taxonomy slugs and the values consist of an array that contains term slugs from the taxonomy referenced in the key. You can list as many terms as you want to be set by default for each taxonomy.

This worked for me on a very plain installation of WordPress 3.0.1. If you know of an alternative method, or think that this code can be improved in any way, please leave a comment.

/**
 * Append the terms of a single taxonomy to the list of
 * classes generated by post_class().
 *
 * @since 2010-07-10
 * @alter 2012-01-06
 */
function mysite_post_class( $classes, $class, $ID ) {

	if ( is_admin() )
		return $classes;

	$taxonomy = 'bananas';

	$terms = get_the_terms( (int) $ID, $taxonomy );
	if ( is_wp_error( $terms ) || empty( $terms ) )
		return $classes;

	foreach ( (array) $terms as $term ) {
		if ( ! in_array( $term->slug, $classes ) )
			$classes[] = $term->slug;
	}

	return $classes;
}

add_filter( 'post_class', 'mysite_post_class', 10, 3 );

It is also possible to add the terms of multiple taxonomies at the same time. All you need to do is pass an array to get_terms() instead of a string. Here’s what it looks like:

/**
 * Append the terms of multiple taxonomies to the list
 * of classes generated by post_class().
 *
 * @since 2010-07-10
 * @alter 2012-01-06
 */
function mysite_post_class( $classes, $class, $ID ) {

	$taxonomies = array(
		'bananas',
		'tacos',
		'bunny-rabbits',
	);

	$terms = get_the_terms( (int) $ID, $taxonomies );

	if ( is_wp_error( $terms ) || empty( $terms ) )
		return $classes;

	foreach ( (array) $terms as $term ) {
		if ( ! in_array( $term->slug, $classes ) )
			$classes[] = $term->slug;
	}

	return $classes;
}

add_filter( 'post_class', 'mysite_post_class', 10, 3 );

if( !function_exists( 'mfields_taxonomy_add_term_row_actions' ) ) {
	add_action( 'admin_init', 'mfields_taxonomy_add_term_row_actions' );
	/**
	 * Dynamically create actions for every defined taxonomy.
	 */
	function mfields_taxonomy_add_term_row_actions() {
		global $wp_taxonomies;
		foreach( $wp_taxonomies as $taxonomy => $taxonomies ) {
			$action = 'manage_' . $taxonomy . '_custom_column';
			add_action( $action, 'your_function_name', 10, 3 );
		}
	}
}

Shorten the Term Descriptions

/**
 * Create actions for all taxonomies.
 *
 * @return    void
 *
 * @since     2010-05-31
 * @alter     2011-01-09
 */
function mfields_taxonomy_description_add_actions() {
	global $wp_taxonomies;
	foreach ( $wp_taxonomies as $taxonomy => $taxonomies ) {
		add_action( 'manage_' . $taxonomy . '_custom_column', 'mfields_taxonomy_description_rows', 10, 3 );
		add_action( 'manage_edit-' . $taxonomy . '_columns',  'mfields_taxonomy_description_columns' );
	}
}
add_action( 'admin_init', 'mfields_taxonomy_description_add_actions' );

/**
 * Filter the taxonomy tables columns.
 *
 * Remove the default "Description" column.
 * Add a custom "Short Description" column.
 *
 * @param     array     Unfiltered columns for the taxonomy's edit screen.
 * @return    array     Modified columns for the taxonomy's edit screen.
 *
 * @since     2010-05-31
 * @alter     2011-01-09
 */
function mfields_taxonomy_description_columns( $c ) {
	unset( $c['description'] );
	$c['short_description'] = 'Description';
	return $c;
}

/**
 * Display the shortened description in each row's custom column.
 *
 * @param     string    Should be empty.
 * @return    string    Name of the column.
 * @return    string    Term id. Integer represented as string.
 *
 * @since     2010-05-31
 * @alter     2011-01-09
 */
function mfields_taxonomy_description_rows( $string, $column_name, $term ) {
	$description = '';
	if ( 'short_description' == $column_name ) {
		global $taxonomy;
		$description = term_description( $term, $taxonomy );
	}
	return $string . mfields_shorten( $description, 40 );
}

/**
 * Shorten a string to a given length.
 *
 * @param     string    The string to shorten.
 * @return    int       Number of characters allowed in $string. Defaults value is 23.
 * @return    string    Text to append to the shortened string.
 *
 * @since     2010-05-31
 * @alter     2011-01-09
 */
function mfields_shorten( $string, $length = 23, $append = '...' ) {
	$string = strip_tags( $string );
	$string = trim( $string );
	$string = html_entity_decode( $string, ENT_QUOTES, 'UTF-8' );
	$string = rtrim( $string, '-' );
	return ( strlen( $string ) > absint( $length ) ) ? substr_replace( $string, $append, absint( $length ) ) : $string;
}

Hope someone finds this useful.

$posts = $wpdb->get_results( "
	SELECT p.*, COUNT( p.`ID` ) AS 'category_count'
	FROM $wpdb->posts AS p, $wpdb->term_taxonomy as tt, $wpdb->term_relationships as tr
	WHERE tt.`taxonomy` = 'category'
	AND tt.`term_taxonomy_id` = tr.`term_taxonomy_id`
	AND tr.`object_id` = p.ID
	AND p.`post_type` = 'post'
	GROUP BY p.`ID`
	HAVING COUNT( p.`ID` ) > 1
	ORDER BY COUNT( p.`ID` ) DESC
	" );

It is quite possible that, if you are installing this plugin on an already existing site, you may have posts that contain more than one category. Since radio buttons allow only one option to be selected at a time, these posts will look like only one category has been assigned while in actuality, there are many. I have created the 1 Post/Category utility which can be accessed via the Tools section of the Administration Menu. Please use this tool to ensure that your posts are in the correct category before allowing other authors to post.

Please note that this plugin only changes the meta box under “Edit”. The “Quick Edit” menu will still use check boxes. I plan on updating this in a future release.

Download

Latest version: Download Radio Categories v0.2 [zip]

Installation

1. Download
2. Unzip the package and upload to your /wp-content/plugins/ directory.
3. Log into WordPress and navigate to the “Plugins” panel.
4. Activate the plugin.

Changelog

0.2

• Now works on WordPress version 2.9.2
• Added support for + “Add New Category”.
• CSS updates for hierarchical category display.
• Moved the 1 Post/Category utility into it’s own file.

0.1

• Original Release – Works on WordPress version 3.0 Beta 2.

if( !function_exists( 'mfields_overwrite_hide_taxonomies_from_admin' ) ) {
	add_action( 'add_meta_boxes', 'mfields_hide_taxonomies_from_admin' );
	function mfields_hide_taxonomies_from_admin() {
		global $wp_taxonomies;
		$hide = array(
			'symbolism'
			);
		foreach( $wp_taxonomies as $name => $taxonomy ) {
			if( in_array( $name, $hide ) ) {
				remove_meta_box( 'tagsdiv-' . $name, 'post', 'side' );
				add_meta_box(
					'mfields_taxonomy_ui_' . $name,
					$taxonomy->label,
					'my_custom_taxonomy_handler_function',
					'post',
					'side',
					'core',
					array( 'taxonomy' => $name )
					);
			}
		}
	}
}

Here’s a screenshot of the plug-in:

The plug-in enables you to display any taxonomy that can be associated with a post (including tags and categories) in any one of 4 different templates: Ordered List, Unordered List, Drop-down Menu and Term Cloud. As with all widgets, you can use multiple instances.

If you have no idea what a taxonomies are and how you can utilize them to their full potential on your own WordPress powered website, please read the following article the I put together on the subject called New and Exciting Ways to Organize Your WordPress Powered Website