Infrastructure plugin which implements metadata functionality for taxonomy terms, including for tags and categories.
This plugin implements the metadata infrastructure for taxonomy terms, so you can add custom metadata (by key) to tags, categories, and other taxonomies. The majority of the code is from sirzooro's submission to the WordPress Core Trac. The rest of the plugin is simply some hacky glue to make this work without modifying the Core. It does not implement any UI for taxonomy term metadata.
The plugin implements the following functions, from which you can build your own custom UI and display code:
add_term_meta($term_id, $meta_key, $meta_value, $unique)
Add meta data field to a term.
delete_term_meta($term_id, $meta_key, $meta_value)
Remove metadata matching criteria from a term. You can match based on the key, or key and value. Removing based on key and value, will keep from removing duplicate metadata with the same key. It also allows removing all metadata matching key, if needed.
get_term_meta($term_id, $key, $single)
Retrieve term meta field for a term.
update_term_meta($term_id, $meta_key, $meta_value, $prev_value)
Update term meta field based on term ID. Use the $prev_value parameter to differentiate between meta fields with the same key and term ID. If the meta field for the term does not exist, it will be added.
Development of this plugin was supported by the Massachusetts Institute of Technology Shakespeare Project.