I'm using a function that changes the front-end and back-end post title for a custom post type according to what you put in certain custom fields.

    //Save ACF fields as post_content for back-end
add_action('save_post', 'change_title_cars');

function change_title_cars($post_id) {
    global $_POST;
    if('cars'== get_post_type()){

      $car_name = get_post_meta($post_id,'car_name',true);
      $first_car_model = ????????????;
      $last_car_model = ????????????;

      $my_post = array();
            $my_post['ID'] = $post_id;
            $my_post['post_title'] = $car_name . ' - ' . $first_car_model . ' ~ ' . $last_car_model;

remove_action('save_post', 'change_title_cars');
                    wp_update_post( $my_post );
add_action('save_post', 'change_title_cars');
    }   
   }


//Save ACF fields as post_content for front-end
add_action('acf/save_post', 'change_title_frontend_cars');

function change_title_frontend_cars($post_id) {
    global $_POST;
    if('cars'== get_post_type()){

      $car_name = get_post_meta($post_id,'car_name',true);
      $first_car_model = ????????????;
      $last_car_model = ????????????;

      $my_post = array();
            $my_post['ID'] = $post_id;
            $my_post['post_title'] = $car_name . ' - ' . $first_car_model . ' ~ ' . $last_car_model;

    remove_action('acf/save_post', 'change_title_frontend_cars');
                    wp_update_post( $my_post );
    add_action('acf/save_post', 'change_title_frontend_cars');
        }
    }

I'm using a repeater which has a sub-field named "car_model". I'm trying to have the title changed into something like this:

(car_name) - (first "car_model" in the repeater) ~ (last "car_model" in the repeater)

but I couldn't get values of the repeater sub-fields inside the function.

Note: the repeater has random number of rows.

I'm using a function that changes the front-end and back-end post title for a custom post type according to what you put in certain custom fields.

    //Save ACF fields as post_content for back-end
add_action('save_post', 'change_title_cars');

function change_title_cars($post_id) {
    global $_POST;
    if('cars'== get_post_type()){

      $car_name = get_post_meta($post_id,'car_name',true);
      $first_car_model = ????????????;
      $last_car_model = ????????????;

      $my_post = array();
            $my_post['ID'] = $post_id;
            $my_post['post_title'] = $car_name . ' - ' . $first_car_model . ' ~ ' . $last_car_model;

remove_action('save_post', 'change_title_cars');
                    wp_update_post( $my_post );
add_action('save_post', 'change_title_cars');
    }   
   }


//Save ACF fields as post_content for front-end
add_action('acf/save_post', 'change_title_frontend_cars');

function change_title_frontend_cars($post_id) {
    global $_POST;
    if('cars'== get_post_type()){

      $car_name = get_post_meta($post_id,'car_name',true);
      $first_car_model = ????????????;
      $last_car_model = ????????????;

      $my_post = array();
            $my_post['ID'] = $post_id;
            $my_post['post_title'] = $car_name . ' - ' . $first_car_model . ' ~ ' . $last_car_model;

    remove_action('acf/save_post', 'change_title_frontend_cars');
                    wp_update_post( $my_post );
    add_action('acf/save_post', 'change_title_frontend_cars');
        }
    }

I'm using a repeater which has a sub-field named "car_model". I'm trying to have the title changed into something like this:

(car_name) - (first "car_model" in the repeater) ~ (last "car_model" in the repeater)

but I couldn't get values of the repeater sub-fields inside the function.

Note: the repeater has random number of rows.

• functions
• custom-field
• advanced-custom-fields

• 1 Have you already checked the docs? You could also do var_dump( get_post_meta( $post_id ) ) to check the metadata list. – Sally CJ Commented Jul 15, 2020 at 8:25
• @sally yes, but I couldn't get it to work. – L. core Commented Jul 15, 2020 at 18:07
• @SallyCJ I hope I understood you correctly, you mean for the repeater, right? I edited the question. – L. core Commented Jul 16, 2020 at 15:11
• No, not really, I just wanted to check the get_post_meta()'s output beforehand. But anyway, I've removed that comment. – Sally CJ Commented Jul 18, 2020 at 8:23
• 1 @SallyCJ Sorry, and thanks anyway. I appreciate giving me your time. – L. core Commented Jul 18, 2020 at 9:54

2 Answers 2

I don't think you need to use save_post to save backend, as acf/save_post also saves when updating the post in the backend. I think (95% sure).

Read the comments below in the code and see if this will help you create the custom post title you are after. Taking into account cars which only have 1 model, multiple models and no models. It's a start anyway.

// run modifications when creating/updating the car post type
add_action('acf/save_post', 'acf_save_car', 20);

/**
 * action to run modifications when creating/updating the car post type
 * @param int $post_id
 * @return void
 */
function acf_save_car($post_id) {

    // get our current global post object data
    global $post;

    // check we are on post type cars else return early
    if($post->post_type <> 'cars') return;

    // if car post status is publish or draft
    if($post->post_status == 'publish' || $post->post_status == 'draft') {

        // create car object from current post object
        $car = $post;

        // get your car name custom field (acf way) and add to title array
        $car_name = get_field('car_name', $post_id);

        // get your model acf repeater field (not sure of field name for repeater)
        $model_data = get_field('car_repeater', $post_id);

        // set model span var as false incase no models exist
        $model_span = false
        
        // if model items exist in repeater
        if($model_data) {

            // create empty models array
            $models = [];
            
            // if only one model exists in repeater
            if(count($model_data) === 1) {
               
                // get the car model name and add it to our array
                $models[] = $model_data[0]['car_model']

            } else {

                // get the first and last model data
                $model_first = current($model_data);
                $model_last = end($model_data);

                // add this data to our model array
                $models[] = $model_first['car_model'];
                $models[] = $model_last['car_model'];

            }
        
            // create our model title segment with squiggly separator  
            $model_span = implode(' ~ ', $models);

        }

        // empty car post title array
        $car_post_title = []
        
        // add car title segments to car post title array if they exist
        $car_name ? $car_post_title[] = $car_name : false;
        $model_span ? $car_post_title[] = $model_span : false;

        // temp remove the save car action
        remove_action('acf/save_post', 'acf_save_car', 20);

        // update our car object with new data
        $car->post_title = implode(' - ', $car_post_title);
        $car->post_name = sanitize_title($car->post_title);
        
        // update the current post with updated car object
        wp_update_post($car);

        // re add the save car action
        add_action('acf/save_post', 'acf_save_car', 20);
    
    }

}

All I needed in my code for it to work is this:

    //get the repeater
    $car_repeater = get_field('repeater_name',$post_id); 
    
    
    $first_row = $car_repeater[0]; //put [0] to get the first row of the repeater
    $first_car_model = $first_row['car_model']; //put [car_model] to get this field value in the specified row (first row)
    
    
    $last_row = end($car_repeater); //use end() to get the last row of the repeater
    $last_car_model = $last_row['car_model']; //put [car_model] to get this field value in the specified row (last row)