Populate a select field according to the value selection in another field

• ahateleybrowne

• July 31, 2020 at 2:37 pm

I’m using JSON to pre-fill a select field with units. But I have a lot of units, so I want to reduce the amount by loading them in disciplines selected in an earlier field. For example, if one selects “Humanities” in field A, I want to get all Humanities units and populate them in field B. I can use the prepare_field filter, and by selecting a discipline, and then saving the post, when I return to it I can get the correct units. But this is obviously clumsy. Can it be done in real time with another filter?

I’ve tried other filters (acf/prepare_field, acf/load_field, acf/format_value) as I’m not confident on their differences, but haven’t had any success yet. Thank you for giving me any steer in the right direction.

/**
 * Filter units by discipline
 */
    
function unitSelection( $unitSelect ) {
    
    if( !isset($_POST['acf']['field_A']) ):
    
		$discipline = get_field( 'discipline') ;

    else:

        $discipline = 'all';

    endif;
    
    // Declare empty array
    $unitSelect['choices'] = array();
    
    // Query with JSON
    $json = file_get_contents('https://college.edu/units/' . $discipline . '/all.json');

    // Convert JSON to an array of posts
    $units = json_decode($json);
    
        foreach ($units as $unit) {
        
            $code = $unit -> unit -> code;
            $title = $unit -> unit -> title;
            
            // Add unit to choices
            $unitSelect['choices'][$code] = $title . ' (' . $code . ')';
            
        }   
    
    // Return the field
    return $unitSelect;
}

add_filter('acf/prepare_field/key=field_B', 'unitSelection');

• John Huebner

• July 31, 2020 at 9:31 pm

This needs to be done by adding JS and AJAX requests, a simple example can be found here https://github.com/Hube2/acf-dynamic-ajax-select-example/tree/master/dynamic-select-example

• ahateleybrowne

• August 1, 2020 at 11:44 am

Thanks John. This looks like it could be an ambitious project for my level. But very keen to give it a crack and learn some new things. Thanks for setting me on the right path! I really appreciate it.