Добавьте файлы проекта.

musicschoolapp/Pages/CourseEditingPage.xaml.cs

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+using Microsoft.Win32;
+using System;
+using System.Collections.Generic;
+using System.Collections.ObjectModel;
+using System.Data.Entity;
+using System.Data.Entity.Infrastructure;
+using System.Data.Entity.Migrations;
+using System.Data.SqlClient;
+using System.Data.SqlTypes;
+using System.Linq;
+using System.Runtime.Remoting.Contexts;
+using System.Text;
+using System.Windows;
+using System.Windows.Controls;
+using System.Windows.Data;
+using System.Windows.Documents;
+using System.Windows.Input;
+using System.Windows.Media;
+using System.Windows.Media.Imaging;
+using System.Windows.Navigation;
+using System.Windows.Shapes;
+using System.IO;
+using System.Data.Entity.Validation;
+
+namespace musicschoolapp.Pages
+{
+    /// <summary>
+    /// Логика взаимодействия для StudentEditingPage.xaml
+    /// </summary>
+    public partial class CourseEditingPage : Page
+    {
+        musicschoolEntities1 mse = new musicschoolEntities1();
+        DbSet<Student> dbContext_;
+        List<Course> students1;
+        bool adding = false;
+        public CourseEditingPage(bool editing)
+        {
+            InitializeComponent();
+            students1 = mse.Course.ToList();
+            dGridStudent.ItemsSource = students1;
+            if(editing)
+            {
+                dGridStudent.IsReadOnly = false;
+            }
+            else
+            {
+                dGridStudent.IsReadOnly = true;
+            }
+        }
+
+
+        public int updateDB()
+        {
+            try
+            {
+                foreach (var student in students1)
+                {
+                    var original = mse.Course.Find(student.CourseID);
+
+                    if (original != null)
+                    {
+                        mse.Entry(original).CurrentValues.SetValues(student);
+                    }
+                    else
+                    {
+                        mse.Course.Add(student);
+                    }
+                }
+                int saveresult = mse.SaveChanges();
+                students1 = mse.Course.ToList();
+                dGridStudent.ItemsSource=students1;
+                return saveresult;
+            }
+            catch (Exception ex)
+            {
+                students1 = mse.Course.ToList();
+                dGridStudent.ItemsSource = students1;
+                return -1;
+            }
+        }
+        private void dGridStudent_MouseDoubleClick(object sender, MouseButtonEventArgs e)
+        {
+            var grid = (DataGrid)sender;
+            var cellInfo = grid.SelectedCells[grid.CurrentCell.Column.DisplayIndex];
+
+            if (cellInfo.Column.Header.ToString() == "Фото")
+            {
+                if (MessageBox.Show("Вы дважды кликнули по столбцу 'Фото'. Изменить?", "Вопрос", MessageBoxButton.YesNo) == MessageBoxResult.Yes)
+                {
+                    OpenFileDialog openFileDialog = new OpenFileDialog();
+                    openFileDialog.ShowDialog();
+                    if (mse.Course.Find((grid.SelectedItem as Course).CourseID) == null)
+                    {
+                        MessageBox.Show("Объект не создан.");
+                        grid.SelectedItem = -1;
+                        mse.Course.Add(dGridStudent.SelectedItem as Course);
+                        try
+                        {
+                            mse.SaveChanges();
+                        }
+                        catch (DbEntityValidationException ex)
+                        {
+                            foreach (var entityValidationErrors in ex.EntityValidationErrors)
+                            {
+                                foreach (var validationError in entityValidationErrors.ValidationErrors)
+                                {
+                                    MessageBox.Show("Свойство: " + validationError.PropertyName + " Ошибка: " + validationError.ErrorMessage);
+                                }
+                            }
+                        }
+
+                        MessageBox.Show("добавил");
+                        int index = grid.SelectedIndex;
+                        grid.SelectedIndex = -1;
+                        grid.SelectedIndex = index;
+                        dGridStudent_SelectionChanged(sender, new SelectionChangedEventArgs(DataGrid.SelectionChangedEvent, new Collection<object> { }, new Collection<object> { dGridStudent.SelectedItem }));
+                    }
+                    mse.SaveChanges();
+                    dGridStudent.ItemsSource = mse.Course.ToList();
+                }
+            }
+        }
+        private void dGridStudent_SelectionChanged(object sender, SelectionChangedEventArgs e)
+        {
+            if (e.AddedItems != null && e.AddedItems.Count > 0)
+            {
+               
+
+            }
+            else if (e.RemovedItems != null && e.RemovedItems.Count > 0)
+            {
+
+                Course selectedStudent = (e.RemovedItems[0] as Course);
+                if (selectedStudent != null)
+                {
+                    Course studentInDb = mse.Course.Find(selectedStudent.CourseID);
+                    if (studentInDb != null)
+                    {
+                        mse.Course.Remove(studentInDb);
+
+                        try
+                        {
+                            mse.SaveChanges();
+                        }
+                        catch (DbUpdateException ex)
+                        {
+
+                            MessageBox.Show("Запись, похоже, удалить нельзя.\n\n" + ex.InnerException);
+                            students1 = mse.Course.ToList();
+                            mse.Entry(studentInDb).State = System.Data.EntityState.Unchanged;
+
+                            return;
+                        }
+                        students1.Remove(dGridStudent.SelectedItem as Course);
+                        dGridStudent.SelectedIndex = -1;
+                        MessageBox.Show("Удалено");
+                    }
+                }
+            }
+
+        }
+    }
+}