WPF + EF.上下文.SaveChanges() 不起作用

我是一个新的WPF开发人员，我正在为一家旅馆编写一个WPF项目。我使用实体框架和数据库优先方法。在UI中，我有一个绑定到学生集合的数据网格。并且宣布了"RowEditEnding"和"AddingNewItem"事件。

所以我想要的只是能够编辑和添加新学生。一切正常，没有错误SaveChanges()但该方法不会将实体保存到数据库中。

我的MainWindow.xaml.cs代码：

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }
    HostelDBEntities db = new HostelDBEntities();
    private bool isInsertMode = false;
    private bool isBeingEdited = false;
    private ObservableCollection<Student> GetStudentsList()
    {
        var list = from e in db.Students select e;
        return new ObservableCollection<Student>(list);
    }
    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        studentsGrid.ItemsSource = GetStudentsList();
    }
    private void studentsGrid_RowEditEnding(object sender, DataGridRowEditEndingEventArgs e)
    {
        Student student = new Student();
        Student st = e.Row.DataContext as Student;
        if (isInsertMode)
        {
            var InsertRecord = MessageBox.Show("Do you want to add a new student?", "Question", MessageBoxButton.YesNo, MessageBoxImage.Question);
            if (InsertRecord == MessageBoxResult.Yes)
            {
                student.FirstName = st.FirstName;
                student.LastName = st.LastName;
                student.Patronymic = st.Patronymic;
                db.Students.Add(student);
                db.SaveChanges();
            }
            else studentsGrid.ItemsSource = GetStudentsList();
        }
        db.SaveChanges();
    }
    private void studentsGrid_AddingNewItem(object sender, AddingNewItemEventArgs e)
    {
        isInsertMode = true;
    }
}

而我的XAML DataGrid代码：

<DataGrid AutoGenerateColumns="False" Name="studentsGrid" Margin="20" ItemsSource="{Binding}"
            RowEditEnding="studentsGrid_RowEditEnding"   AddingNewItem="studentsGrid_AddingNewItem" >
    <DataGrid.Columns>
        <DataGridTextColumn Binding="{Binding StudentId, NotifyOnSourceUpdated=True, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Header="StudentId" IsReadOnly="True" />
        <DataGridTextColumn Binding="{Binding FirstName, NotifyOnSourceUpdated=True, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Header="First Name" />
        <DataGridTextColumn Binding="{Binding Patronymic, NotifyOnSourceUpdated=True, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Header="Patronymic" />
        <DataGridTextColumn Binding="{Binding LastName, NotifyOnSourceUpdated=True, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" Header="Last Name" />
    </DataGrid.Columns>
</DataGrid>

谁能帮我了解如何解决它？创建上下文以保存对数据库的更改。

谢谢。