protected function get_group_member_ids() {
		global $wpdb;

		if ( is_array( $this->group_member_ids ) ) {
			return $this->group_member_ids;
		}

		$bp  = buddypress();
		$sql = array(
			'select'  => "SELECT user_id FROM {$bp->groups->table_name_members}",
			'where'   => array(),
			'orderby' => '',
			'order'   => '',
		);

		/* WHERE clauses *****************************************************/

		// Group id.
		$group_ids = wp_parse_id_list( $this->query_vars['group_id'] );
		$group_ids = implode( ',', $group_ids );
		$sql['where'][] = "group_id IN ({$group_ids})";

		// If is_confirmed.
		$is_confirmed = ! empty( $this->query_vars['is_confirmed'] ) ? 1 : 0;
		$sql['where'][] = $wpdb->prepare( "is_confirmed = %d", $is_confirmed );

		// If invite_sent.
		if ( ! is_null( $this->query_vars['invite_sent'] ) ) {
			$invite_sent = ! empty( $this->query_vars['invite_sent'] ) ? 1 : 0;
			$sql['where'][] = $wpdb->prepare( "invite_sent = %d", $invite_sent );
		}

		// If inviter_id.
		if ( ! is_null( $this->query_vars['inviter_id'] ) ) {
			$inviter_id = $this->query_vars['inviter_id'];

			// Empty: inviter_id = 0. (pass false, 0, or empty array).
			if ( empty( $inviter_id ) ) {
				$sql['where'][] = "inviter_id = 0";

			// The string 'any' matches any non-zero value (inviter_id != 0).
			} elseif ( 'any' === $inviter_id ) {
				$sql['where'][] = "inviter_id != 0";

			// Assume that a list of inviter IDs has been passed.
			} else {
				// Parse and sanitize.
				$inviter_ids = wp_parse_id_list( $inviter_id );
				if ( ! empty( $inviter_ids ) ) {
					$inviter_ids_sql = implode( ',', $inviter_ids );
					$sql['where'][] = "inviter_id IN ({$inviter_ids_sql})";
				}
			}
		}

		// Role information is stored as follows: admins have
		// is_admin = 1, mods have is_mod = 1, banned have is_banned =
		// 1, and members have all three set to 0.
		$roles = !empty( $this->query_vars['group_role'] ) ? $this->query_vars['group_role'] : array();
		if ( is_string( $roles ) ) {
			$roles = explode( ',', $roles );
		}

		// Sanitize: Only 'admin', 'mod', 'member', and 'banned' are valid.
		$allowed_roles = array( 'admin', 'mod', 'member', 'banned' );
		foreach ( $roles as $role_key => $role_value ) {
			if ( ! in_array( $role_value, $allowed_roles ) ) {
				unset( $roles[ $role_key ] );
			}
		}

		$roles = array_unique( $roles );

		// When querying for a set of roles containing 'member' (for
		// which there is no dedicated is_ column), figure out a list
		// of columns *not* to match.
		$roles_sql = '';
		if ( in_array( 'member', $roles ) ) {
			$role_columns = array();
			foreach ( array_diff( $allowed_roles, $roles ) as $excluded_role ) {
				$role_columns[] = 'is_' . $excluded_role . ' = 0';
			}

			if ( ! empty( $role_columns ) ) {
				$roles_sql = '(' . implode( ' AND ', $role_columns ) . ')';
			}

		// When querying for a set of roles *not* containing 'member',
		// simply construct a list of is_* = 1 clauses.
		} else {
			$role_columns = array();
			foreach ( $roles as $role ) {
				$role_columns[] = 'is_' . $role . ' = 1';
			}

			if ( ! empty( $role_columns ) ) {
				$roles_sql = '(' . implode( ' OR ', $role_columns ) . ')';
			}
		}

		if ( ! empty( $roles_sql ) ) {
			$sql['where'][] = $roles_sql;
		}

		$sql['where'] = ! empty( $sql['where'] ) ? 'WHERE ' . implode( ' AND ', $sql['where'] ) : '';

		// We fetch group members in order of last_joined, regardless
		// of 'type'. If the 'type' value is not 'last_joined' or
		// 'first_joined', the order will be overridden in
		// BP_Group_Member_Query::set_orderby().
		$sql['orderby'] = "ORDER BY date_modified";
		$sql['order']   = 'first_joined' === $this->query_vars['type'] ? 'ASC' : 'DESC';

		$group_member_ids = $wpdb->get_col( "{$sql['select']} {$sql['where']} {$sql['orderby']} {$sql['order']}" );

		$invited_member_ids = array();

		// If appropriate, fetch invitations and add them to the results.
		if ( ! $is_confirmed || ! is_null( $this->query_vars['invite_sent'] ) || ! is_null( $this->query_vars['inviter_id'] ) ) {
			$invite_args = array(
				'item_id' => $this->query_vars['group_id'],
				'fields'  => 'user_ids',
				'type'    => 'all',
			);

			if ( ! is_null( $this->query_vars['invite_sent'] ) ) {
				$invite_args['invite_sent'] = ! empty( $this->query_vars['invite_sent'] ) ? 'sent' : 'draft';
			}

			// If inviter_id.
			if ( ! is_null( $this->query_vars['inviter_id'] ) ) {
				$inviter_id = $this->query_vars['inviter_id'];

				// Empty: inviter_id = 0. (pass false, 0, or empty array).
				if ( empty( $inviter_id ) ) {
					$invite_args['type'] = 'request';

				/*
				* The string 'any' matches any non-zero value (inviter_id != 0).
				* These are invitations, not requests.
				*/
				} elseif ( 'any' === $inviter_id ) {
					$invite_args['type'] = 'invite';

				// Assume that a list of inviter IDs has been passed.
				} else {
					$invite_args['type'] = 'invite';
					// Parse and sanitize.
					$inviter_ids = wp_parse_id_list( $inviter_id );
					if ( ! empty( $inviter_ids ) ) {
						$invite_args['inviter_id'] = $inviter_ids;
					}
				}
			}

			/*
			 * If first_joined is the "type" of query, sort the oldest
			 * requests and invitations to the top.
			 */
			if ( 'first_joined' === $this->query_vars['type'] ) {
				$invite_args['order_by']   = 'date_modified';
				$invite_args['sort_order'] = 'ASC';
			}

			$invited_member_ids = groups_get_invites( $invite_args );
		}

		$this->group_member_ids = array_merge( $group_member_ids, $invited_member_ids );

		/**
		 * Filters the member IDs for the current group member query.
		 *
		 * Use this filter to build a custom query (such as when you've
		 * defined a custom 'type').
		 *
		 * @since 2.0.0
		 *
		 * @param array                 $group_member_ids Array of associated member IDs.
		 * @param BP_Group_Member_Query $this             Current BP_Group_Member_Query instance.
		 */
		$this->group_member_ids = apply_filters( 'bp_group_member_query_group_member_ids', $this->group_member_ids, $this );

		return $this->group_member_ids;
	}