There have been many times we have wanted to use taxonomies as a 1-to-1 ratio with a post or custom post types. This is arguably more effective than using metadata because as Alex King pointed out, using a taxonomy query is more efficient than using a meta query, not to mention all the other cool things that are done by default with custom taxonomies (i.e. admin columns).
This snippet replaces the default taxonomy checkbox select metabox for hierarchical taxonomies with a radio select metabox, which effectively limits your taxonomy selection to one term. Just include this file from your functions.php or plugin file and update the parameters at the bottom.
Note: A radio select metabox will get out of hand quickly if more than a few terms are needed.
Update: Helen Housandi was kind enough to look over our snippet and provide some feedback. Thanks to that, there are some pretty awesome improvements to the class.
Update 2: Code is now on Github. Forks/pull requests welcome.
<?php
if ( !class_exists( 'WDS_Taxonomy_Radio' ) ) {
/**
* Removes and replaces the built-in taxonomy metabox with our radio-select metabox.
* @link http://codex.wordpress.org/Function_Reference/add_meta_box#Parameters
*/
class WDS_Taxonomy_Radio {
// Post types where metabox should be replaced (defaults to all post_types associated with taxonomy)
public $post_types = array();
// Taxonomy slug
public $slug = '';
// Taxonomy object
public $taxonomy = false;
// New metabox title. Defaults to Taxonomy name
public $metabox_title = '';
// Metabox priority. (vertical placement)
// 'high', 'core', 'default' or 'low'
public $priority = 'high';
// Metabox position. (column placement)
// 'normal', 'advanced', or 'side'
public $context = 'side';
// Set to true to hide "None" option & force a term selection
public $force_selection = false;
/**
* Initiates our metabox action
* @param string $tax_slug Taxonomy slug
* @param array $post_types post-types to display custom metabox
*/
public function __construct( $tax_slug, $post_types = array() ) {
$this->slug = $tax_slug;
$this->post_types = is_array( $post_types ) ? $post_types : array( $post_types );
add_action( 'add_meta_boxes', array( $this, 'add_radio_box' ) );
}
/**
* Removes and replaces the built-in taxonomy metabox with our own.
*/
public function add_radio_box() {
foreach ( $this->post_types() as $key => $cpt ) {
// remove default category type metabox
remove_meta_box( $this->slug .'div', $cpt, 'side' );
// remove default tag type metabox
remove_meta_box( 'tagsdiv-'.$this->slug, $cpt, 'side' );
// add our custom radio box
add_meta_box( $this->slug .'_radio', $this->metabox_title(), array( $this, 'radio_box' ), $cpt, $this->context, $this->priority );
}
}
/**
* Displays our taxonomy radio box metabox
*/
public function radio_box() {
// uses same noncename as default box so no save_post hook needed
wp_nonce_field( 'taxonomy_'. $this->slug, 'taxonomy_noncename' );
// get terms associated with this post
$names = wp_get_object_terms( get_the_ID(), $this->slug );
// get all terms in this taxonomy
$terms = (array) get_terms( $this->slug, 'hide_empty=0' );
// filter the ids out of the terms
$existing = ( !is_wp_error( $names ) && !empty( $names ) )
? (array) wp_list_pluck( $names, 'term_id' )
: array();
// Check if taxonomy is hierarchical
// Terms are saved differently between types
$h = $this->taxonomy()->hierarchical;
// default value
$default_val = $h ? 0 : '';
// input name
$name = $h ? 'tax_input['. $this->slug .'][]' : 'tax_input['. $this->slug .']';
echo '<div style="margin-bottom: 5px;">
<ul id="'. $this->slug .'_taxradiolist" data-wp-lists="list:'. $this->slug .'_tax" class="categorychecklist form-no-clear">';
// If 'category,' force a selection, or force_selection is true
if ( $this->slug != 'category' && !$this->force_selection ) {
// our radio for selecting none
echo '<li id="'. $this->slug .'_tax-0"><label><input value="'. $default_val .'" type="radio" name="'. $name .'" id="in-'. $this->slug .'_tax-0" ';
checked( empty( $existing ) );
echo '> '. sprintf( __( 'No %s', 'wds' ), $this->taxonomy()->labels->singular_name ) .'</label></li>';
}
// loop our terms and check if they're associated with this post
foreach ( $terms as $term ) {
$val = $h ? $term->term_id : $term->slug;
echo '<li id="'. $this->slug .'_tax-'. $term->term_id .'"><label><input value="'. $val .'" type="radio" name="'. $name .'" id="in-'. $this->slug .'_tax-'. $term->term_id .'" ';
// if so, they get "checked"
checked( !empty( $existing ) && in_array( $term->term_id, $existing ) );
echo '> '. $term->name .'</label></li>';
}
echo '</ul></div>';
}
/**
* Gets the taxonomy object from the slug
* @return object Taxonomy object
*/
public function taxonomy() {
$this->taxonomy = $this->taxonomy ? $this->taxonomy : get_taxonomy( $this->slug );
return $this->taxonomy;
}
/**
* Gets the taxonomy's associated post_types
* @return array Taxonomy's associated post_types
*/
public function post_types() {
$this->post_types = !empty( $this->post_types ) ? $this->post_types : $this->taxonomy()->object_type;
return $this->post_types;
}
/**
* Gets the metabox title from the taxonomy object's labels (or uses the passed in title)
* @return string Metabox title
*/
public function metabox_title() {
$this->metabox_title = !empty( $this->metabox_title ) ? $this->metabox_title : $this->taxonomy()->labels->name;
return $this->metabox_title;
}
}
$custom_tax_mb = new WDS_Taxonomy_Radio( 'custom-tax-slug' );
// Update optional properties
// $custom_tax_mb->priority = 'low';
// $custom_tax_mb->context = 'normal';
// $custom_tax_mb->metabox_title = __( 'Custom Metabox Title', 'yourtheme' );
// $custom_tax_mb->force_selection = true;
}
View or fork on github.