Primary Term

A WordPress plugin that allows you to enter select a primary term (tag, category, etc.) for a post.

Added Bonus: If you use this plugin with the category taxonomy and have %category% part of your permalink structure, the primary category will be used in your permalink. Also, if you use the Breadcrumb NavXT plugin for breadcrumbs it will use the primary category in the breadcrumbs as well.

Installation

• Download into your plugins directory (e.g. /wp-content/plugins)

Displaying primary term in your theme

To retrieve the name of the primary term

$term_name = apply_filters( 'ac_get_primary_term', '' );

To display the name of the primary term

do_action( 'ac_primary_term' );

To display the name of the primary term as a link pointing to its archive URL

do_action( 'ac_primary_term', true );

To retrieve the primary tag of a post for your own processing

if ( class_exists( 'AC_Primary_Term' ) {
    $primary_tag_id = AC_Primary_Tag::get_primary_term( $post_id )
}

Using another taxonomy, label or post meta key

All of these three variables have filters applied so you can set them without modifying the plugin code:

Example of how to change the meta key

function ac_primary_tag_post_meta_key( $var ) {
    return 'your_custom_post_meta_key';
}
add_filter( 'ac_primary_tag_post_meta_key', 'ac_primary_tag_post_meta_key', 10, 1 );

Example of how to change the taxonomy

function ac_primary_tag_taxonomy( $var ) {
    return 'category';
}
add_filter( 'ac_primary_tag_taxonomy', 'ac_primary_tag_taxonomy', 10, 1 );

Example of how to change the label of the dropdown

function ac_primary_tag_taxonomy_nice_name( $var ) {
    return 'Post Category';
}
add_filter( 'ac_primary_tag_taxonomy_nice_name', 'ac_primary_tag_taxonomy_nice_name', 10, 1 );

Known Issues

• On export to XML and subsequent import the term id may not be the same
• Not sure how to deal with a situation when a post is not tagged with a term that is selected to be primary. We could hook into javascript, potentially but when javascript isn't enabled in the browser we'd need to disable this feature as well

Credits

Methods that add the metabox and save value submitted are largely copied and pasted from the Codex (http://codex.wordpress.org/Function_Reference/add_meta_box)