Deleting Cars

This article is relevant to entity models that utilize the deprecated Visual Studio integration of Telerik Data Access. The current documentation of the Data Access framework is available here.

You will now add functionality to MainForm to delete existing cars.

1. In the code behind of MainForm define a new property SelectedCar. It will be used to retrieve the car which is currently selected in the RadGridView control of the form.

   private Car SelectedCar
   {
       get
       {
           return this.carsBindingSource.Current as Car;
       }
   }
   

   Private ReadOnly Property SelectedCar() As Car
       Get
           Return Me._carsBindingSource.Current
       End Get
   End Property
   

2. In the Design view of MainForm double click the Delete button to generate its Click event handler. Here a confirmation dialog is shown and depending on the result from it the delete operation is performed. If the deletion is successful, the data displayed in the grid is refreshed by the PopulateBindingSource() method, if not a message is shown.

   private void rbtnDeleteCar_Click(object sender, EventArgs e)
   {
       Car selectedCar = this.SelectedCar;
       if (selectedCar == null)
       {
           RadMessageBox.Show("You must first select a car in order to delete it!",
                              "Warning", 
                               MessageBoxButtons.OK, 
                               RadMessageIcon.Exclamation);
           return;
       }
       DialogResult deleteConfirmation = RadMessageBox.Show(string.Format("You are about to delete {0} {1}. Are you sure?",
                                                            selectedCar.Make,
                                                            selectedCar.Model),
                                                   "Confirm delete", 
                                                   MessageBoxButtons.YesNo,
                                                   RadMessageIcon.Question);
       if (deleteConfirmation != DialogResult.Yes)
       {
           return;
       }
       this.context.Delete(selectedCar);
       bool saveChangesIsSuccessful = false;
       try
       {
           this.context.SaveChanges();
           saveChangesIsSuccessful = true;
       }
       catch (DataStoreException ex)
       {
           RadMessageBox.Show("Could not delete this car entry" +  
                              "because other entries related to it" + 
                              " exist in the database. Exception message: \n\r" + 
                               ex.BackendError.Description,
                         "Error", 
                          MessageBoxButtons.OK, 
                          RadMessageIcon.Error);
       }
       catch (Exception ex)
       {
           RadMessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, RadMessageIcon.Error);
       }
       if (saveChangesIsSuccessful)
       {
           this.PopulateBindingSource();
       }
   } 
   

   Private Sub rbtnDeleteCar_Click(sender As Object, e As EventArgs) Handles rbtnDeleteCar.Click
       Dim selectedCar As Car = Me.SelectedCar
       If IsNothing(selectedCar) Then
           RadMessageBox.Show("You must first select a car in order to delete it!",
                              "Warning", 
                               MessageBoxButtons.OK, 
                               RadMessageIcon.Exclamation)
           Exit Sub
       End If
       Dim deleteConfirmation As DialogResult = RadMessageBox.Show(String.Format("You are about to delete {0} {1}. Are you sure?", 
                                                                   selectedCar.Make, 
                                                                   selectedCar.Model),
                                                       "Confirm delete",
                                                       MessageBoxButtons.YesNo,
                                                       RadMessageIcon.Question)
       If deleteConfirmation <> DialogResult.Yes Then
           Exit Sub
       End If
       Me._context.Delete(selectedCar)
       Dim saveChangesIsSuccessfull As Boolean = False
       Try
           Me._context.SaveChanges()
           saveChangesIsSuccessfull = True
       Catch ex As DataStoreException
           RadMessageBox.Show("Could not delete this car entry" + 
                              " because other entries related to it" + 
                              " exist in the database. Exception message:" + 
                   vbCrLf + ex.BackendError.Description,
                   "Error", MessageBoxButtons.OK, RadMessageIcon.Error)
       Catch ex As Exception
           RadMessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK, RadMessageIcon.Error)
       End Try
       If saveChangesIsSuccessfull Then
           Me.PopulateBindingSource()
       End If
   End Sub
   

Checkpoint

You can now delete existing cars through MainForm.

Next Step: Editing and Adding Cars to the Database