public func fetchCourses() -> Single<[MbyCourse]> {
        return Single.create { [unowned self] single in
            do {
                var fetchCourses: [MbyCourse] = []
                //                let chapters: [Org]!
                try self.dbPool.read { db in
                    fetchCourses = try MbyCourse.fetchAll(db)
                }
                single(.success(fetchCourses))
            } catch {
                print("error: \(error)")
                single(.error(error))
            }
            return Disposables.create {}
        }
    }