/// <summary>
        /// Добавление студента в журнал
        /// </summary>
        /// <param name="elGradebookGroupStudent"></param>
        /// <returns></returns>
        public async Task AddElGradebookGroupStudent(ElGradebookGroupStudent elGradebookGroupStudent)
        {
            // Добавляем записи с оценками в случае наличия занятий
            var lessons = await GetElGradebookWithLessonsAsync(elGradebookGroupStudent.ElGradebookId);

            if (lessons != null)
            {
                elGradebookGroupStudent.ElGradebookLessonMarks = new List <ElGradebookLessonMark>();
                foreach (var lesson in lessons.ElGradebookLessons)
                {
                    elGradebookGroupStudent.ElGradebookLessonMarks
                    .Add(new ElGradebookLessonMark {
                        ElGradebookLessonId = lesson.ElGradebookLessonId, ElGradebookLessonAttendanceTypeId = 1
                    });
                }
            }

            _context.Add(elGradebookGroupStudent);
            await _context.SaveChangesAsync();
        }
        /// <summary>
        /// Редактирование студента в списке группы электронного журнала
        /// </summary>
        /// <param name="elGradebookGroupStudent"></param>
        /// <returns></returns>
        public async Task UpdateElGradebookGroupStudent(ElGradebookGroupStudent elGradebookGroupStudent)
        {
            var entry = await GetElGradebookGroupStudentAsync(elGradebookGroupStudent.ElGradebookGroupStudentId);

            if (entry == null)
            {
                throw new Exception("Студент не найден!");
            }

            if (entry.ElGradebookGroupStudentFio != elGradebookGroupStudent.ElGradebookGroupStudentFio)
            {
                entry.ElGradebookGroupStudentFio = elGradebookGroupStudent.ElGradebookGroupStudentFio;
            }

            if (entry.AppUserId != elGradebookGroupStudent.AppUserId)
            {
                entry.AppUserId = elGradebookGroupStudent.AppUserId;
            }

            _context.Update(entry);
            await _context.SaveChangesAsync();
        }