Remove Subcategories from WordPress Permalinks

WordPress has great flexibility when it comes to specifying your permalink structure. I had a request come in recently, however, to use only the topmost category in the permalinks for a site. The settings did not seem to allow this, so I had to find a way to remove subcategories from WordPress permalinks.

No Code

You can get the permalink structure to use just the top-level category, but it requires active participation of the authors, and would require you to edit all existing posts. If you’re starting a brand new site, you can use /%category%/ for the permalink structure. However, with every post, you’ll need to select the subcategory for the post and it’s top-most parent category. WordPress will then be able to find the post by either permalink, with or without the subcategory in the URL.

This is a perfectly acceptable solution, if you have complete control over every post and don’t mind ensuring every parent category is selected on those posts. And if you don’t mind the answering the inevitable question when an author forgets to tick that top-most level category.

Remove Subcategories from WordPress Permalinks, Every Time

To ensure the subcategories are removed without user intervention, we’re going to have to get our hands dirty. With PHP. Get it? I already did a bit of Googling, and found this StackOverflow post, which gave me a handle on the overall approach. So my hands are dirty here, too.

Let’s take a look at the code.

add_filter( 'post_link', 'my_filter_post_link' );
 
function my_get_all_child_categories( $category_id ) {
 
  $subcategories = array();
 
  $category = get_category( $category_id );
  if ( $category->parent ) {
    $subcategories[] = $category->slug . '/';
    $results = my_get_all_child_categories( $category->parent );
    $subcategories = array_merge( $subcategories, $results );
  }
 
  return $subcategories;
}
 
function my_filter_post_link( $permalink, $post, $leavename ) {
 
  if ( 'post' != get_post_type( $post ) )
    return $permalink;
 
  switch ( $post->post_type ) {
    case 'post':
 
      $categories = get_the_category( $post->ID );
      $subcategories = array();
 
      foreach ( $categories as $category ) {
        $results = my_get_all_child_categories( $category->term_id );
        $subcategories = array_merge( $subcategories, $results );
      }
 
      $permalink = str_replace( $subcategories, '', $permalink );
 
      break;
  }
 
  return $permalink;
}

We’re going to need to hook into the post_link filter and do a little bit of recursion. Evaluating the filter hook function, we can see we’re limiting our logic to basic post types. We then use our custom my_get_all_child_categories function to get an array of child category slugs with their trailing slashes.

Once we have all the subcategories in an array, we can simply use str_replace to clean up the post permalink.

Violà! We now completely remove subcategories from WordPress permalinks!