How to add a default item to a custom taxonomy?

Question

Wordpress default taxonomy (Categories) has the item Uncategorized by default. How to add a default item to a new custom taxonomy?

functions.php:

// === CUSTOM TAXONOMIES === //
function my_custom_taxonomies() {
    register_taxonomy(
        'block',        // internal name = machine-readable taxonomy name
        'static_content',       // object type = post, page, link, or custom post-type
        array(
            'hierarchical' => true,
            'labels' => array(
                'name' => __( 'Blocks' ),
                'singular_name' => __( 'Block' ),
                'add_new_item' => 'Add New Block',
                'edit_item' => 'Edit Block',
                'new_item' => 'New Block',
                'search_items' => 'Search Block',
                'not_found' => 'No Block found',
                'not_found_in_trash' => 'No Block found in trash',
            ),
            'query_var' => true,    // enable taxonomy-specific querying
            'rewrite' => array( 'slug' => 'block' ),    // pretty permalinks for your taxonomy?
        )
    );
}
add_action('init', 'my_custom_taxonomies', 0);

EDIT: I just want to have the taxonomy item there when the theme is installed. It doesn't have to automatically be added to any empty term.

Answer 1

Have a look here:

https://web.archive.org/web/20150403012347/http://wordpress.mfields.org/2010/set-default-terms-for-your-custom-taxonomies-in-wordpress-3-0/

Basically what you need to do is use the save_post hook to check the terms for the post and add the default term from your taxonomy if it's empty.

If you just want to have an initial term set in your custom taxonomy, then you can use wp_insert_term(). Probably easiest to add it in the same function that you're using to create your custom taxonomy. As t3ios adds in the comments, you should call get_term() first, and only insert the term if the return value is null (ie the term doesn't exist).

This example code is from the Codex: http://codex.wordpress.org/Function_Reference/wp_insert_term

$parent_term = term_exists( 'fruits', 'product' ); // array is returned if taxonomy is given
$parent_term_id = $parent_term['term_id']; // get numeric term id
wp_insert_term(
  'Apple', // the term 
  'product', // the taxonomy
  array(
    'description'=> 'A yummy apple.', 
    'slug' => 'apple', 
    'parent'=> $parent_term_id
  )
);

Answer 2

Update as of 2020

Version	Description
5.5.0	Introduced default_term argument.

Since Wordpress version 5.5.0 release, you're now able to specify a default term when registering a new custom taxonomy using the very handy default_term argument.

$args = [
    /...
    'default_term' => [ //(string|array) Default term to be used for the taxonomy.
        'name' => 'Potato', //(string) Name of default term.
        'slug' => 'potato', //(string) Slug for default term.
        'description' => 'You can spend the night inside a potato, https://www.youtube.com/watch?v=h2mj-7-Zklw', //(string) Description for default term.
    ],
    /...
];

Answer 3

Default category is hardcoded case in wp_insert_post() function.

So it can't be replicated exactly, but you can handle it in other ways. I'd try to hook into post status transition for new posts and assign wanted default term if none were assigned during post creation.

Answer 4

I needed to populate a Custom Taxonomy "Days" with the days of the week..I did not want the client to have to mess with creating days, or get in there and delete days or misspell days. Following the above advice I came up with this, but I am wondering if there is a more concise way of coding it:

 /*************************************** ...Create a Custom Taxonomy for days ******************************/
add_action( 'init', 'build_taxonomies', 0 );  
function build_taxonomies() {  
    register_taxonomy( 
    'days', 
    'schedule',
   array( 'hierarchical' => true, 
    'label' => 'Days',
    'query_var' => true, 
    'show_ui' => false, //removes the menus from admin menu and edit panel  
    'rewrite' => true ) );  

/*---------------------------------------Check to see if the days are created..if not, create them----*/
$parent_term = term_exists( 'days', 'days' ); // array is returned if taxonomy is given
$parent_term_id = $parent_term['term_id']; // get numeric term id

wp_insert_term(//this should probably be an array, but I kept getting errors..
        'Monday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'monday',
        'parent'=> $parent_term_id ));

wp_insert_term(
        'Tuesday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'tuesday',
        'parent'=> $parent_term_id ));

wp_insert_term(
        'Wednesday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'wednesday',
        'parent'=> $parent_term_id ));

wp_insert_term(
        'Thursday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'thursday',
        'parent'=> $parent_term_id ));

wp_insert_term(
        'Friday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'friday',
        'parent'=> $parent_term_id ));

wp_insert_term(
        'Saturday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'saturday',
        'parent'=> $parent_term_id ));

wp_insert_term(
        'Sunday', // the term 
        'days', // the taxonomy
        array(
        'slug' => 'sunday',
        'parent'=> $parent_term_id ));
}
/************ now I add my own meta box for days to get rid of extra controls *************/

add_action('admin_menu', 'add_custom_categories_box');
function add_custom_categories_box() {
 add_meta_box('myrelateddiv', 'Days*', 'ilc_post_related_meta_box', 'schedule', 'normal', 'low', array( 'taxonomy' => 'days' ));
}

function ilc_post_related_meta_box( $post, $box ) {
  $defaults = array('taxonomy' => 'related');
  if ( !isset($box['args']) || !is_array($box['args']) )
  $args = array();
  else
  $args = $box['args'];
  extract( wp_parse_args($args, $defaults), EXTR_SKIP );
  $tax = get_taxonomy($taxonomy);
?>

  <ul id="<?php echo $taxonomy; ?>checklist" class="list:<?php echo $taxonomy?> categorychecklist form-no-clear">
<?php
  wp_terms_checklist($post->ID, array( 'taxonomy' => $taxonomy, 'popular_cats' => $popular_ids, 'checked_ontop' => FALSE ) )
?>
</ul>   

Answer 5

Using the Default Term plugin you could do this

register_taxonomy( 'custom-tax', array('post'), array(
    'label'              => 'Custom Tag',
    'public'             => true,
    'show_ui'            => true,
    'default_term'       => 'Some Default Term', // Add this line to your code 
// then activate and deactivate the default term plugin to save the terms you set.
));

By default when the post is submitted it will save the default term to the post if there are no term checked. It works for both hierarchical and non hierarchical taxonomies.