public void AddStudentToCourse(Student Student, string Course) { if (Student.Courses.Any(c => c.Course.Name == Course)) { return; } var db_course = _Courses.GetByName(Course); if (db_course is null) { throw new InvalidOperationException($"Курс {Course} отсутствует в базе данных"); } Student.Courses.Add(new StudentCourse(Student, db_course)); _Students.SaveChanges(); }