Insert value to database on signup

Hi Roland,

This question is a follow up from this thread.

How do you insert information a user enters on a signup form to the database when the submit button is pressed?

In the thread linked above you helped me creating a custom dropdown field and now im struggling arround to get that selected value back to the database as soon as the submit button is pressed.

At the moment I have this code for my custom dropdown:

<?php
global $wpdb;
$field = 'activity_title';
$activities = array();
// grab the unique stored values from the field
$result = $wpdb->get_results('SELECT DISTINCT p.' . $field . ' from ' . Participants_Db::$participants_table . ' p WHERE p.' . $field . ' <> "" AND p.approved ="yes"', ARRAY_N);
// now we convert the query result into a simple array
foreach($result as $value) {
  $activities[] = current($value);
}
// print the dropdown
echo PDb_FormElement::get_element(array(
    'name' => 'selected_activity',
    'type' => 'dropdown',
    'options' => $activities
        )
    );
?>

To get the information from the selected dropdown value back to the database I was starting to use code like this:

$table_name = Participants_Db::$participants_table;
$wpdb->insert($table_name, array('activity_title' => $_POST['selected_activity']));

Can you help me that the selected value from the dropdown is inserted to the database when the submit button is pressed?

Thanks and regards,
Mario

https://ww.wp.xz.cn/plugins/participants-database/