Limiting the number of users

3 comments

1. As you can see in the WordPress Option Reference, there’s an option called users_can_register. You can – per default – set it in your (network-)sites settings.

   • 1 => Yes
   • 0 => No

   As usual: There’s a filter to intercept that from a plugin.

   "option_{$option_name}"
   

   So you can simply attach a callback to this filter and check the amount of users with a WP_User_Query for the get_current_blog_id().

   <?php
   
   namespace WPSE;
   /** Plugin Name: WPSE (#110036) Limit Total Users per page */
   defined( 'ABSPATH' ) or exit;
   
   add_filter( 'option_users_can_register', 'limit_total_users' );
   function limit_total_users( $option )
   {
       // Nothing to do here
       if ( 0 === $option )
           return $option;
   
       static $users = null;
       $limit = 50;
   
       if ( null === $users )
       {
           $users_query = new WP_User_Query( array(
               'blog_id' => get_current_blog_id()
           ) );
           $users = $users_query->get_total();
       }
   
       // Abort if we're above the limit
       if ( $limit > $users )
           return 0;
   
       return $option;
   }
   

   The nice thing about this mini plugin is, that it doesn’t do an additional query if the registration is already turned off.

2. Piggybacking off Kaiser’s answer:

   add_filter( 'option_users_can_register', 'limit_total_users' );
   function limit_total_users( $option )
   {
       // Registration turned off manually. Nothing to do here.
       if ( 0 === $option )
           return $option;
   
       $user_count = count_users();
   
       // Abort if we're above the limit
       if ( $user_count['total_users'] > 50 ) {
           return 0;
       } 
   
       // The threshold wasn't reached yet.
       return $option;
   }
   

   Interesting bit of info on that count_users() function is it actually returns an array with a count for each role. You may wish to identify which role you are limiting, or simply add/subtract to account for the difference in, for example, the number of admins – as you may not wish to count yourself in the total.

3. This solution differs from the others in that the primary work in done on user registration. After a user registers the total users are counted and the users_can_register option is updated if necessary. That seems to be the best way to minimize front-end processing time. A related function hooked to pre_option_users_can_register prevents blog admins from cheating by toggling the switch in “General Settings” and getting an extra user thereby. Technically only that function is necessary but I have explained the reasons for the other function.

   function count_reg_users_wpse_110036() {
     global $wpdb;
     $users = $wpdb->get_var("SELECT COUNT(ID) FROM {$wpdb->users}");
     return $users;
   }
   
   function limit_users_wpse_110036() {
     $count = apply_filters('limit_user_count',4);
     $users = count_reg_users_wpse_110036();
     if ($users >= $count) {
       update_option('users_can_register',0);
     }
   }
   add_action('user_register','limit_users_wpse_110036');
   
   function limit_user_option_wpse_110036($option) {
     remove_filter('pre_option_users_can_register','limit_user_option_wpse_110036');
     $reg = get_option('users_can_register');
     if (0 === $reg) {
       return 0;
     }
     $count = apply_filters('limit_user_count',4);
     $users = count_reg_users_wpse_110036();
     if ($users >= $count) {
       update_option('users_can_register',0);
       return 0;
     } else {
       return $option;
     }
   }
   add_filter('pre_option_users_can_register','limit_user_option_wpse_110036');
   

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