Custom permalink for one category

Question

I have the following permalink structure /%category%/blog/%postname%/.

I also have an archive at /blog which lists all blog posts.

I have one particular category for which I'd like the permalink structure to be /blog/%postname%/

This is the code I've tried :

add_filter( 'post_link', 'custom_permalink', 10, 3 );
function custom_permalink( $permalink, $post, $leavename ) {

$category = get_the_category($post->ID); 
if (  !empty($category) && $category[0]->cat_name == "hello" ) {
    $permalink = trailingslashit( home_url('/blog/'. $post->post_name 
.'/' ) );
}
return $permalink;
}

This first part works correctly and changes the url of the post with category 'hello' to https://example/blog/post-name - In the next part I'm trying to create a redirect for this url to the actual post.

add_action('generate_rewrite_rules', 'custom_rewrite_rules');
function custom_rewrite_rules( $wp_rewrite ) {

$feed_rules = array(

  '^blog/?' => 'index.php?name=$matches[1]',
);
$wp_rewrite->rules = $feed_rules + $wp_rewrite->rules;
return $wp_rewrite->rules;;
}

This also works and redirects the url to https://example/blog/post-name But! this url, instead of showing a single post - is showing my blog archive, so is rendering essentially the same as - https://example/blog/

My question - why is https://example/blog/post-name showing the same as https://example/blog/ rather than showing the post?

Answer 1

Your rewrite rule doesn't capture anything. Change:

'^blog/?'

to add the capture group you reference with $matches[1] in your rule:

'^blog/([^/]+)/?'

visit the Settings > Permalinks page, which will flush rules, and your code should otherwise work.

Answer 2

First of all, I see a problem in your code you should know about, instead of using rewrite_rules_array which is final rewrite rules filter, or even something like post_rewrite_rules you using action generate_rewrite_rules to put your own rules accessing globally and changing $wp_rewrite. You better to use one of the suitable filters, like in this example.

add_filter( 'rewrite_rules_array', function( $rules ){
    $rule = [ '^blog/([^/]+)/?' => 'index.php?name=$matches[1]' ];
    return array_merge( $rule, $rules);
});