Change a field's value during submission based on another value

Created by Phil Kurth, Modified on Thu, 16 Feb, 2023 at 8:28 AM by Phil Kurth

At present, there isn't a convenient filter in place to do this so if you need to modify a field value during submission, you need to modify the $_POST superglobal directly.

// Note the priority of 5 used on this hook. This is so that the modification fires before Advanced Forms' handler which
// fires on a priority of 10.
add_action( 'init', function () {

	// Make sure a form was posted.
	if ( ! isset( $_POST['af_form'] ) ) {
		return;
	}

	// Check for the form key to only run this on a specific form.
	if ( $_POST['af_form'] !== 'form_63603dfd5f7d2' ) {
		return;
	}

	$field_1_key = 'field_63603df414f2a';
	$field_2_key = 'field_63603e7514f2b';

	// Check the value of field 1 matches a condition and if so, modify the value of field 2.
	if ( isset( $_POST['acf'][ $field_1_key ] ) and $_POST['acf'][ $field_1_key ] === 'some value' ) {
		$_POST['acf'][ $field_2_key ] = 'field 2 updated value';
	}

}, 5 );