Primary Category is a plugin that allows publishers to designate a primary category for posts, and query for posts by their primary category.
When adding more than one category, you are given the option of selecting which category is the primary one:
This plugin extends WP_Query by adding a new parameter, primary_category, that accepts the category ID to get posts that have that as their primary category.
$args = array(
'primary_category' => 4,
);
$query = new WP_Query( $args );The Primary Category plugin registers a private taxonomy that keeps track of which category is currently the primary one. When you search by primary category, the plugin uses tax_query to find the posts that have that primary category set.
Why use a taxonomy and not post meta? Post meta is great for storing unique metadata about a post, but its not efficient for querying. Taxonomies are great for grouping posts, and querying by them is faster.
With over 5+ million active installations, the Yoast SEO plugin is one of the most popular plugins in the WordPress plugin directory. Yoast SEO has its own "primary category" functionality that it uses for (among other things) determining which category to show in the breadcrumbs.
Primary Category detects if the Yoast SEO plugin is installed and will use the UI it provides. This ensures there aren't multiple "make primary" buttons shown.
Note: Yoast SEO stores their primary category as post meta, and is not meant for querying (which is why you should use this plugin!).
By default, only users who can edit the current post can set the primary category. This plugin provides a filter called user_can_set_primary_category that allows you to set your own security rules.
function only_admin_can_edit_primary_category() {
return current_user_can( 'manage_options' );
}
add_filter( 'user_can_set_primary_category', 'only_admin_can_edit_primary_category' );