title: WooCommerce admin order edit save post
body: <p>In WooCommerce, when I submit, how to catch a custom select field added in the order edit admin pages?</p>
  
  <p>I have added this custom select field in the file <code>class-wc-meta-box-order-data.php</code>. I get this:</p>
  
  <p><a href="https://i.stack.imgur.com/yeOIG.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yeOIG.jpg" alt="enter image description here"></a></p>
  
  <p>But I dont know how to catch or to save <code>$_POST['vendor']</code></p>
  
  <p>I have tried to add <code>$_POST['vendor']</code> in <code>wp-admin/post.php</code> ，<strong>but it doesn't work</strong>.</p>
  
  <p>This is the code that I have added:</p>
  
  <pre><code>    &lt;select class="wc-customer-search" id="customer_user" name="customer_user" data-placeholder="&lt;?php esc_attr_e( 'Guest', 'woocommerce' ); ?&gt;" data-allow_clear="true"&gt;
                                  &lt;option value="&lt;?php echo esc_attr( $user_id ); ?&gt;" selected="selected"&gt;&lt;?php echo htmlspecialchars( $user_string ); ?&gt;&lt;/option&gt;
                              &lt;/select&gt;
                              &lt;!--/email_off--&gt;
                          &lt;/p&gt;
                     &lt;p&gt; &lt;label for="order_status"&gt;供應商： &lt;/label&gt;
                      &lt;select name="vendor"&gt;
    &lt;?php 
             global $wpdb;
     $user_count = $wpdb-&gt;get_var( "SELECT COUNT(*) FROM $wpdb-&gt;users" );
      for($i=1;$i&lt;=$user_count;$i++){
      $user_info = get_userdata($i);
  
      if (implode(', ', $user_info-&gt;roles)=='vendor')
  echo "&lt;option value=".$user_info-&gt;user_login."&gt;$user_info-&gt;user_login&lt;/option&gt;";
      }
                      ?&gt;
  &lt;/select&gt;&lt;/p&gt; 
  </code></pre>
  
  <p>How can I get the submitted value and how can I save it?</p>