Custom post-type in root directory, blog posts in subdirectory

Question

I have a website with one custom post type as well as a blog.

For the custom post type I would like to have the slug as root, like so

http://domain.com/<title>

And the blog post I would like to display under /blog, like so

http://domain.com/blog/<title>

I've managed to "minimize" the custom post type's urls by using these two functions:

add_filter( 'post_type_link', function($post_link, $post, $leavename) {
    if('custom' == $post->post_type && 'publish' == $post->post_status) {
        $post_link = str_replace( '/' . $post->post_type . '/', '/', $post_link);
        return $post_link;
    }

    return $post_link;

}, 10, 3 );

and

add_action('pre_get_posts', function($query) {
    if ( ! $query->is_main_query() || 3 != count( $query->query ) || ! isset( $query->query['page'] ) ) {
        return;
    }

    if ( ! empty( $query->query['name'] ) ) {
        $query->set( 'post_type', array( 'post', 'custom', 'page' ) );
    }
});

However, I have not managed to move my blog posts to /blog.

I've tried to set the permalink structure to

/blog/%postname%/

and the custom post type's rewrite to

'rewrite' => array('slug' => 'custom', 'with_front' => false)

However, this does not produce the desired effect (domain.com/title). Instead, the "custom" slug is now part of the url again. Manually removing it (domain.com/title) produces a 404.

Answer 1

moving blog posts to /blog/ is pretty easy and you can use WordPress settings to do that - no coding needed.

The problem you will have though is that after moving posts, your CPT URL structure will conflict with URL structure of pages - so you'll have to modify your pre_get_posts function.

As for your post_type_link you can simplify it a lot (if it is not hierarchical... is it?):

add_filter( 'post_type_link', function($post_link, $post, $leavename) {
    if ('custom' == $post->post_type && 'publish' == $post->post_status) {
        $post_link = site_url('/') . $post->post_name .'/';
    }

    return $post_link;

}, 10, 3 );

And I also wouldn't use pre_get_posts for selecting proper posts. Using parse_request is a lot easier for this task and it allows you to prevent 404 errors a lot easier.

add_action( 'parse_request', function ( $wp ) {
    if ( ! is_admin() ) {
        if ( array_key_exists('error', $wp->query_vars) && '404' == $wp->query_vars['error'] ) {
            $custom_post = get_page_by_path( $wp->request, OBJECT, 'CUSTOM' );

            if ( $custom_post instanceof WP_Post ) {
                unset( $wp->query_vars['error'] );
                $wp->query_vars['page'] = '';
                $wp->query_vars['CUSTOM'] = $wp->query_vars['name'] = $wp->request;
                $wp->query_vars['post_type'] = 'CUSTOM';
            }            
        }
    }

    return $wp;
} );