private void UpdateCourses(object sender, SelectionChangedEventArgs e)
        {
            if (DepartmentsComboBox.SelectedIndex == -1)
            {
                CoursesComboBox.ItemsSource = null;
                return;
            }

            var sqlParams = new[]
            {
                new SqlParameter
                {
                    ParameterName = "@DepartmentId",
                    Value         = Departments[DepartmentsComboBox.SelectedIndex].DepartmentId
                }
            };

            var courses = SqlServer.SqlServer.ExecuteStoredProcedure(_connectionString, _userCredential,
                                                                     "GetCoursesByDepartment", "Courses", sqlParams).Tables["Courses"].Rows;

            Courses = Course.GetCollection(courses);

            CoursesComboBox.ItemsSource = Courses.Select(c => c.CourseName).ToList();
        }