How to assign a value to a taxonomy without showing it in the form in front-end?

For my understanding,
- $post->post_id must be the current post id,
- get_queried_object_id() is the id of the custom taxonomy to be set
- $taxonomy_slug is the value to be given to the taxonomy.
Right?

How do I point here to the current post id?

For the rest, it should look like
add_action( 'rwmb_frontend_after_save_post', function( $post ) {
wp_set_object_terms( $post->post_id, 123, "Amsterdam" );
} );
where 123 is the id of the location taxonomy.
Is that correct?

Where do I specify that action hook? Close to or with the [mb_frontend_form id="xxx"] command?

It's obvious I am not a code writer...

I'm a bit puzzled: to set a value to the taxonomy should I use the rwmb_frontend_after_save_post or rwmb_frontend_after_process?

I think I understand your code
add_action( 'rwmb_frontend_after_process', function( $config, $post_id ) {
if ( 'xxx' === $config['id'] ) {
wp_set_object_terms( $post_id, get_queried_object_id(), 'location' );
}
}, 10, 2 );

What I don't understand yet is:
- how to give a value ("Amsterdam") to the location
- how to give a value specific to the current page to the location, as I will have a page per location.
Does it take it from the current location of the page? (location taxonomy is also attached to pages).

I have to set this php code in the functions.php file, right?

Hi Long,

Back to my original question:
"I have a form for a CPT, and I have a custom taxonomy (=location) assigned to that CPT, but the taxonomy is not part of the form. That is because each location has its own page showing the form in the front-end, and I do not want to bother the visitor selecting the location.

How to assign the value for that location to the taxonomy-field when the user submits a new custom post, so that at another webpage (with an archive view) all custom posts for that location can be shown?"

your approach forces me to have a metabox for each location, while I was working towards 1 metabox for the cpt, and the taxonomy location assigned to it, but not being part of the metabox. Isn't there a way to achieve it with 1 metabox for the cpt?

In your showcase, the term for the location is shown to the visitor, while I want it to be hidden.
So wouldn't a hidden field with the value for the location in each metabox be better?

Anyway, when I follow each step of your example, I see the following happening:
- in the admin area I see both Amsterdam and Rotterdam as fields assigned to each post of cpt Work Place, see https://share.getcloudapp.com/WnuJm6kr.
Probably because I have set both metaboxes to cpt Work Place, but I assume it needs to be set there, right?
- but the location remains empty (https://share.getcloudapp.com/p9uGeZmZ), although I have copied your php code in the snippet (https://share.getcloudapp.com/2Nuybp9E) and included the snippet shortcode in the page (https://share.getcloudapp.com/2Nuybpog).
Hence it seems not to be working.

What I didn't mention is that the same (location) taxonomy is assigned to the page. I have a page for each location, with the [mb_frontend_form] command. My thought was that this [mb_frontend_form] can be the same on each page, and that the location can be derived from the taxonomy of the page.

Is there not a way to obtain the taxonomy value of the page and assign that to the taxonomy of the cpt?
That way, just one meta box would work for all locations.

Back to your showcase with Work Place: still the location is not set. It remains empty.
Any advice?

Hi Long,

Excellent, now it's all working!

Thanks so much for your help.