public function populate_extras() {
		global $wpdb;

		// Bail if no users.
		if ( empty( $this->user_ids ) || empty( $this->results ) ) {
			return;
		}

		// Bail if the populate_extras flag is set to false
		// In the case of the 'popular' sort type, we force
		// populate_extras to true, because we need the friend counts.
		if ( 'popular' == $this->query_vars['type'] ) {
			$this->query_vars['populate_extras'] = 1;
		}

		if ( ! (bool) $this->query_vars['populate_extras'] ) {
			return;
		}

		// Turn user ID's into a query-usable, comma separated value.
		$user_ids_sql = implode( ',', wp_parse_id_list( $this->user_ids ) );

		/**
		 * Allows users to independently populate custom extras.
		 *
		 * Note that anything you add here should query using $user_ids_sql, to
		 * avoid running multiple queries per user in the loop.
		 *
		 * Two BuddyPress components currently do this:
		 * - XProfile: To override display names.
		 * - Friends:  To set whether or not a user is the current users friend.
		 *
		 * @see bp_xprofile_filter_user_query_populate_extras()
		 * @see bp_friends_filter_user_query_populate_extras()
		 *
		 * @since 1.7.0
		 *
		 * @param BP_User_Query $this         Current BP_User_Query instance.
		 * @param string        $user_ids_sql Comma-separated string of user IDs.
		 */
		do_action_ref_array( 'bp_user_query_populate_extras', array( $this, $user_ids_sql ) );

		// Fetch last_active data from the activity table.
		$last_activities = BP_Core_User::get_last_activity( $this->user_ids );

		// Set a last_activity value for each user, even if it's empty.
		foreach ( $this->results as $user_id => $user ) {
			$user_last_activity = isset( $last_activities[ $user_id ] ) ? $last_activities[ $user_id ]['date_recorded'] : '';
			$this->results[ $user_id ]->last_activity = $user_last_activity;
		}

		// Fetch usermeta data
		// We want the three following pieces of info from usermeta:
		// - friend count
		// - latest update.
		$total_friend_count_key = bp_get_user_meta_key( 'total_friend_count' );
		$bp_latest_update_key   = bp_get_user_meta_key( 'bp_latest_update'   );

		// Total_friend_count must be set for each user, even if its
		// value is 0.
		foreach ( $this->results as $uindex => $user ) {
			$this->results[$uindex]->total_friend_count = 0;
		}

		// Create, prepare, and run the separate usermeta query.
		$user_metas = $wpdb->get_results( $wpdb->prepare( "SELECT user_id, meta_key, meta_value FROM {$wpdb->usermeta} WHERE meta_key IN (%s,%s) AND user_id IN ({$user_ids_sql})", $total_friend_count_key, $bp_latest_update_key ) );

		// The $members_template global expects the index key to be different
		// from the meta_key in some cases, so we rejig things here.
		foreach ( $user_metas as $user_meta ) {
			switch ( $user_meta->meta_key ) {
				case $total_friend_count_key :
					$key = 'total_friend_count';
					break;

				case $bp_latest_update_key :
					$key = 'latest_update';
					break;
			}

			if ( isset( $this->results[ $user_meta->user_id ] ) ) {
				$this->results[ $user_meta->user_id ]->{$key} = $user_meta->meta_value;
			}
		}

		// When meta_key or meta_value have been passed to the query,
		// fetch the resulting values for use in the template functions.
		if ( ! empty( $this->query_vars['meta_key'] ) ) {
			$meta_sql = array(
				'select' => "SELECT user_id, meta_key, meta_value",
				'from'   => "FROM $wpdb->usermeta",
				'where'  => $wpdb->prepare( "WHERE meta_key = %s", $this->query_vars['meta_key'] )
			);

			if ( false !== $this->query_vars['meta_value'] ) {
				$meta_sql['where'] .= $wpdb->prepare( " AND meta_value = %s", $this->query_vars['meta_value'] );
			}

			$metas = $wpdb->get_results( "{$meta_sql['select']} {$meta_sql['from']} {$meta_sql['where']}" );

			if ( ! empty( $metas ) ) {
				foreach ( $metas as $meta ) {
					if ( isset( $this->results[ $meta->user_id ] ) ) {
						$this->results[ $meta->user_id ]->meta_key = $meta->meta_key;

						if ( ! empty( $meta->meta_value ) ) {
							$this->results[ $meta->user_id ]->meta_value = $meta->meta_value;
						}
					}
				}
			}
		}
	}