Vb.Net獲取數據表中的最後一個自動增量值

Question

我正在從數據表名車表中加載來自訪問數據庫的數據。此表具有carId爲自動增加的編號

加載數據是這樣的：

Private Sub frmCar_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
    Try 
     dsDataSet = New DataSet 
     loadCars() 

     bsCar = New BindingSource(dsDataSet, "car") 

     CarIDTextBox.DataBindings.Add(New Binding("text", bsCar, "carId")) 
     BrandTextBox.DataBindings.Add(New Binding("text", bsCar, "brand")) 
     ModelTextBox.DataBindings.Add(New Binding("text", bsCar, "model")) 
     RegNoTextBox.DataBindings.Add(New Binding("text", bsCar, "regNo")) 
     InsIDTextBox.DataBindings.Add(New Binding("text", bsCar, "insId")) 
     DailyChargeTextBox.DataBindings.Add(New Binding("text", bsCar, "dailyCharge")) 
     WeeklyChargeTextBox.DataBindings.Add(New Binding("text", bsCar, "weeklyCharge")) 
     MonthlyChargeTextBox.DataBindings.Add(New Binding("text", bsCar, "monthlyCharge")) 
     YearlyChargeTextBox.DataBindings.Add(New Binding("text", bsCar, "yearlyCharge")) 
     TransmissionTextBox.DataBindings.Add(New Binding("text", bsCar, "transmission")) 
     ColorTextBox.DataBindings.Add(New Binding("text", bsCar, "color")) 
     RemarkTextBox.DataBindings.Add(New Binding("text", bsCar, "remark")) 


    Catch ex As Exception 
     MsgBox(Err.Description) 
    End Try 
End Sub 

Sub loadCars() 
    Dim sql As String 

    Try 
     oledbConn = New OleDbConnection(oledbConnString) 
     oledbConn.Open() 

     sql = "select * from car order by carId" 
     daCar = New OleDbDataAdapter(sql, oledbConn) 
     daCar.Fill(dsDataSet, "car") 
     '---------------------------------------------------------------------- 

     oledbConn.Close() 
    Catch ex As Exception 
     oledbConn.Close() 
     MsgBox(Err.Description) 
    End Try 
End Sub 

Private Sub btnNew_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNew.Click 
    Try 
     bsCar.AddNew() 

    Catch ex As Exception 
     MsgBox(Err.Description) 
    End Try 
End Sub 

Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click 
    Try 
     Me.Validate() 
     bsCar.EndEdit() 
     daCar.Update(dsDataSet.Tables("car")) 
     MsgBox("Car saved successfully") 
    Catch ex As Exception 
     MsgBox(Err.Description) 
    End Try 
End Sub 

現在，當我添加一個新的汽車，並保存它，一切都運行完美。但是我需要添加的新車的車型在添加後立即顯示。我怎麼能不查詢數據庫？謝謝

Answer 1

在執行Update方法的過程中，似乎有辦法從數據庫中獲取AutoIncrement值，但是沒有辦法避免對數據庫進行其他查詢。
在更新（或插入）行後，您可以使用OleDbDataAdapter引發的RowUpdated事件。

我們需要使用Access支持的「SELECT @@ IDENTITY」命令，但如果我們不在Update所使用的同一連接上工作，則這種方法無效，因此唯一的選擇是使用RowUpdated事件連接仍然打開

' Need to have a OleDbCommandBuilder to build the InsertCommand for the OleDbDataAdapter 
Sub loadCars() 
    .... 
    daCar = New OleDbDataAdapter(sql, oledbConn) 
    Dim builder = new OleDbCommandBuilder(daCar) 
    daCar.InsertCommand = builder.GetInsertCommand 
    daCar.Fill(dsDataSet, "car") 
End Sub 


' In the update code 
AddHandler daCar.RowUpdated, New OleDbRowUpdatedEventHandler(AddressOf NewRowInserted) 
daCar.Update(dsDataSet.Tables("car")) 

' The event handler is called for any row inserted, updated or deleted 
Sub NewRowInserted(sender as Object, e as OleDb.OleDbRowUpdatedEventArgs) 

    ' Check if we are working for a row with the proper state 
    If e.Row.RowState = DataRowState.Added Then 
     Dim cmd = new OleDbCommand("SELECT @@IDENTITY",e.Command.Connection) 
     Dim newID = DirectCast(cmd.ExecuteScalar(), Integer) 
     Console.WriteLine(newID) 
    End If 
End Sub