Data Access with ADO.NET in .NET

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Data Access with ADO.NET
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dr.CancelEdit() dr.BeginEdit() End If dt.DefaultView.RowFilter = emp_id= & newId & BindTable() End Sub
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This code sets a RowFilter to the added row. This ensures that the correct row will be in edit mode and no other rows are available to distract the user. Finally, the Cancel method is modified to delete the new row if the Cancel button has been clicked. This code follows:
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Private Sub dgEmployee_CancelCommand( _ ByVal source As Object, _ ByVal e As System.Web.UI.WebControls.DataGridCommandEventArgs) _ Handles dgEmployee.CancelCommand dgEmployee.EditItemIndex = -1 Get the DataTable from the Session. Dim dt As DataTable = CType(Session( Employee ), DataTable) Get the DataRow to be canceled. Dim PrimaryKey As String = dgEmployee.DataKeys(e.Item.DataSetIndex) would be better if this was an autonumber If PrimaryKey = *NEW ID* Then Dim dr As DataRow = dt.Rows.Find(PrimaryKey) dt.Rows.Remove(dr) End If dt.DefaultView.RowFilter = BindTable() End Sub
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Figure 8.10 shows the Add method in action. Notice that when the Add button is clicked, the DataGrid automatically resizes to a single row, which is the row that is being added. The only thing left is to allow the deletion of DataRows.
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Figure 8.10 The Add button in action.
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Deleting a DataRow with the DataGrid
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Deleting a DataRow with the DataGrid is a relatively easy task. A Delete button column and a little bit of code are needed to handle the button. The new Delete button code follows:
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Dim colDel As New ButtonColumn() colDel.CommandName = Delete colDel.Text = Delete colDel.ButtonType = ButtonColumnType.PushButton colDel.ItemStyle.Width = New Unit(colWidth, UnitType.Pixel) dgEmployee.Columns.Add(colDel)
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This code adds a ButtonColumn and sets the button type to a PushButton. The next code snippet shows the code for the Delete button.
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Private Sub dgEmployee_DeleteCommand( _ ByVal source As Object, _ ByVal e As System.Web.UI.WebControls.DataGridCommandEventArgs) _ Handles dgEmployee.DeleteCommand Get the DataTable from the Session. Dim dt As DataTable = CType(Session( Employee ), DataTable) Get the DataRow to be updated. Dim PrimaryKey As String = dgEmployee.DataKeys(e.Item.DataSetIndex) Dim dr As DataRow = dt.Rows.Find(PrimaryKey) dr.CancelEdit() Delete the row. dr.Delete() dt.DefaultView.RowFilter = dgEmployee.EditItemIndex = -1 dgEmployee.SelectedIndex = -1 BindTable() End Sub
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This code locates the DataRow and marks it for deletion. The last items ensure that the RowFilter is clear and no Item is being edited. The completed DataGrid with the Delete button is shown in Figure 8.11.
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Updating the Data Store
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Until now, all data modification has been done in a local DataTable or DataSet. This section examines several methods of updating the data store. The DataGrid from the previous section will be used as a graphical interface for these operations.
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Data Access with ADO.NET
Figure 8.11 The completed DataGrid contains the Add, Edit, and Delete buttons.
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The DataAdapter can be used to update the data store. The DataAdapter requires select, insert, update, and delete commands to successfully send changes back to the data store. Rather that create each of these commands, ADO.NET offers a class called the CommandBuilder, which can create the insert, update, and delete commands as long as the select command has been supplied. The command builder can only be used when the data store that is being updated represents a single table. In this example, a command button is placed in the header of the delete column. When the command button is clicked, the UpdateDB method is executed. The following code shows the UpdateDB button.
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Dim colDel As New ButtonColumn() colDel.HeaderText = _ <input type= submit runat= server & _ name= dgEmployee:UpdateAll value= Update DB /> colDel.CommandName = Delete colDel.Text = Delete colDel.ButtonType = ButtonColumnType.PushButton colDel.ItemStyle.Width = New Unit(colWidth, UnitType.Pixel) dgEmployee.Columns.Add(colDel)
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The Page Load method has been modified to called the UpdateDB method, as shown in the following code:
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Private Sub Page_Load( _ ByVal sender As System.Object, _ ByVal e As System.EventArgs) Handles MyBase.Load If Not IsPostBack Then BindTable() ElseIf Request( dgEmployee:Add ) = Add Then AddEmployee()
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ElseIf Request( dgEmployee:UpdateAll ) = Update DB Then UpdateDB() End If End Sub
Finally, the UpdateDB method contains the code to modify the data store. This code follows:
Public Sub UpdateDB() Dim dt As DataTable If Not Session( Employee ) Is Nothing Then Dim cnstr As String = integrated security=yes;database=pubs Dim cn As New SqlConnection(cnstr) Dim sql As String = Select * from employee Dim daEmployee As New SqlDataAdapter(sql, cn) Dim cmdBld As New SqlCommandBuilder(daEmployee) dt = CType(Session( Employee ), DataTable) daEmployee.Update(dt) End If BindTable() End Sub
This code starts by connecting to the Session variable that contains the DataTable. Next, the connection and DataAdapter are created. Finally, a CommandBuilder is created, which will create the insert, update, and delete commands automatically when required. The finished Web page is shown in Figure 8.12.
Although the CommandBuilder object was used in the example, separate command objects may be assigned to each of the DataAdapter s commands. The commands may contain calls to stored procedures as well.