Hierarchical select for native Advanced Custom Fields taxonomy fields.

custom-acf-admin.js

jQuery(document).ready(function($){

	//Modify select2 ajax request to include a parent_id parameter, used by custom_acf_taxonomy_hierarchy()
	acf.add_filter('select2_ajax_data', function( data, args, $input, field, instance ){

		var target_field_key = 'field_5c7634ca3413f'; //YOUR TARGET FIELD KEY HERE

		if(data.field_key == target_field_key){

			var parent_id = 0; //by default we want terms with parent of 0 (top level)
			
			if($input.val() != '' && $input.val() != null){ //if we have chosen one or more terms already
				var values = $input.val();
				parent_id = values.pop(); //get last selected term to use as the parent for the next query
			}
	
			data.parent = parent_id;
		}

	  return data;

	});
	
});

hierearchical-select-acf.php

<?php

//Modifies ajax requests from our select2 dropdown, $args = WP_Term_Query arguments
function custom_acf_taxonomy_hierarchy( $args, $field, $post_id ){
    //default to 0 (top-level terms only) unless we get a different parent with the request
    $args['parent'] = empty($_POST['parent']) ? 0 : $_POST['parent'];
    
    //To allow multiple top-level selections, we can go back to the top of the taxonomy tree after we reach the end of a branch
    /*
    if(!empty($args['parent'])){
        $child_terms = get_term_children($args['parent'],'YOUR_TAXONOMY_SLUG'); //change to your taxonomy slug
        if(empty($child_terms) || is_wp_error($child_terms)) $args['parent'] = 0;
    }
    */
    
    return $args;
}
add_filter('acf/fields/taxonomy/query/key=field_5c7634ca3413f', 'custom_acf_taxonomy_hierarchy',10,3);


//Make the javascript available in the admin when editing a post with ACF
function custom_admin_enqueue_scripts(){        
    wp_enqueue_script('custom-acf-admin-js', get_stylesheet_directory_uri() . '/js/custom-acf-admin.js',['jquery']);
}
add_action('acf/input/admin_enqueue_scripts','custom_admin_enqueue_scripts');

To get ALL selected values use this:
data.all_selected = Object.values( collections ); // Get all selected options

Updated the JS with a simpler way to get the value(s) you already selected.

$input is the taxonomy field you are working with, so $input.val() will give you a simple array of selected term ids. From there you can pop() the most recent value off to use as your parent.

Any updates on this one? I also have the same problem as @gb3000..

@HobbyAlchemist I have updated the code since then, but have not tested it extremely recently. You'll need to debug your own javascript and see what's going on, there's not too many moving parts there. Make sure you are targeting the correct field (use your own field key on line 5 of the JS)

Ok! Thank you! Found another way using fields with child taxonomy and conditional logic setup againts a choice select box. A bit more work, but gets the job done.

This is helpful. I was in the same issue with @HobbyAlchemist and @gb3000. I solved replacing
add_action('admin_enqueue_scripts','custom_admin_enqueue_scripts');
with
add_action('acf/input/admin_enqueue_scripts','custom_admin_enqueue_scripts');
I would really love this if it allows me to do the multiple select. When I reach the end of the hierachy it shows "no results found" and doesnt come back to ask for parent anymore. Is there a way?
Thanks!

Thanks for the better Javascript hook @ArneSaknussemm - updated.

In case you didn't work out how to allow multiple values, just add a check to custom_acf_taxonomy_hierarchy() to see if the given parent id has any child terms (get_term_children()) and override it with 0 if not. This makes you follow a branch of the taxonomy tree to the end, then go back to the top.

Thanks so much for sharing this! It is a lifesaver!
Regarding allowing multiple terms, → aka going to the top level if it runs out of children.
Would it be possible that you add the lines you have mentioned in the last post.
I am pretty new to PHP & JS, so your help would be highly appreciated.

@albertvisuals Sure thing, done. Just uncomment it and change the taxonomy slug to your own, tested and working for me.

@MogulChris Thanks very much for your help!!!! You've saved my day :)

Hello everyone, I've been looking for this solution for the past two days, Great I've found it but am not good at PHP and jQuery.

Am using ACF Frontend to allow users to submit their products via a frontend form.

after reading some articles on how to use jQuery in WP, I create a js folder in my child theme directory and uploaded the jQuery file. (customized the field key and also I didn't change the naming of the js file.)

I added the PHP code to the functions.php of my child theme but there is no change.

I'd request you guys to help me out on how to make it work. Thank you

Is it possible not working anymore under ACF Version 6.0.5 and/or PHP 8.1? Has somebody an idea why?
Thanks a lot!

albertvisuals

FOund some workaround/fix?