How auto update db from datagrid - wpf

Question

I am using VB/wpf and SQL Server. I am NOT using mvvm, a datatable, a button, a dataset or a windows form. Under those conditions and a couple of days of searching, I cannot find the final step to saving the data from a grid.
My database table tracks donations; it has the usual, expected fields. Here is what I have so far:
XAML (snippet):
<Window.Resources>
<CollectionViewSource
Filter="Filter_By_Member"
x:Key="cvsDonations">
</CollectionViewSource>
.....
<DataGrid
AutoGenerateColumns="False"
CanUserReorderColumns="True"
CanUserResizeColumns="True"
CanUserResizeRows="False"
CanUserDeleteRows="True"
FontSize="13"
FontWeight="Normal"
ItemsSource="{Binding Source={StaticResource cvsDonations}}"
Name="dgDonations"
RowHeaderWidth="20"
SelectionUnit="CellOrRowHeader"
SelectionMode="Single">
<DataGrid.Columns>
<DataGridTextColumn
Binding="{Binding Path=DateDue, Converter={StaticResource conDate}, StringFormat='MMM d, yyyy'}"
ElementStyle="{StaticResource styDateBlock}"
Header="Date Due"
IsReadOnly="True"
Width="90">
</DataGridTextColumn>
.....
My window contains a ComboBox and the grid. The rows in the grid depend on what is selected in the ComboBox. Here is the code that does that.
Private Sub Change_Member(sender As Object, e As SelectionChangedEventArgs) Handles cboMembers.SelectionChanged
cvsDonations.View.Refresh()
End Sub
Private Sub Filter_By_Member(sender As Object, e As FilterEventArgs)
Dim PersonID As Long = CLng(cboMembers.SelectedValue)
Dim d As Donation = DirectCast(e.Item, Donation)
If d.PersonID = PersonID Then
e.Accepted = True
Else
e.Accepted = False
End If
End Sub
So far everything works. What I haven't figured out is how to automatically update the underlying database (using stored procedures which are already written and working). More specifically, I cannot figure out what event to watch for and how to implement that event in code.
The underlying collection is an ObservableCollection(Of Donation) and the Donation class has implemented INotifyPropertyChanged. I've considered watching the property changed but that event gets fired every time the grid is populated so that doesn't seem like the right approach, besides I can't figure out how to actually raise the appropriate event even if that is the way to go.
I've tried using the RowEditChanging event which seems to be ALMOST what I want but it is fired before any edits are submitted so the donation the row contains has the old value when this event is fired.
What is the right approach and how should it be implemented given my overall set up?

Answer 1

I suggest doing it this way -
Your Donation class should have a flag field, let's say Is_Dirty which keeps track of whether the object has modifications or not.
When you initially load items in your collection, make sure Is_Dirty is set to false. When user makes edit on grid and property notification is fired, set the dirty flag (from property setter).
For saving, I suggest having a separate button, clicking on which you go through all dirty objects from your collection and pass updates to database.
By binding to dirty flag, you can also change the appearance of modified rows for user to identify modified rows.
You can also maintain a State property, to know whether the object is Added, Updated or Deleted.
Typically, I put all this functionality in a base class from which all my model classes (e.g. Donation) derives.
Some snippet to get you going...
public abstract class ObservableDomainObject : INotifyPropertyChanged
{
public event PropertyChangedEventHandler PropertyChanged;
private bool _isDirty;
public ObservableDomainObject()
{
_state = ObjectState.Added;
_isDirty = true;
}
private ObjectState _state;
/// <summary>
/// Get or Set
/// </summary>
public ObjectState State
{
get { return _state; }
set
{
if (_state != value)
{
_state = value;
RaisePropertyChanged();
}
}
}
public void SetDirty(Boolean isDirty)
{
this.IsDirty = isDirty;
}
/// <summary>
/// Check if the object is modified.
/// </summary>
public bool IsDirty
{
get { return _isDirty; }
set
{
if (_isDirty != value)
{
if (_state != ObjectState.Added && _state != ObjectState.Deleted)
{
this.State = value ? ObjectState.Modified : ObjectState.Unchanged;
}
_isDirty = value;
RaisePropertyChanged();
}
}
}
protected virtual void RaisePropertyChanged([System.Runtime.CompilerServices.CallerMemberName] string propertyName = "")
{
PropertyChangedEventHandler handler = this.PropertyChanged;
if (handler != null)
{
handler(this, new PropertyChangedEventArgs(propertyName));
}
// Change Dirty flag when property changed.
if (propertyName != "IsDirty")
SetDirty(true);
}
}
public enum ObjectState
{
/// <summary>
/// New Record
/// </summary>
Added = 0,
/// <summary>
/// Unchanged after the load
/// </summary>
Unchanged,
/// <summary>
/// Modified
/// </summary>
Modified,
/// <summary>
/// Deleted
/// </summary>
Deleted
}