Working with Session

Postback and Variables Variables declared in a web page including ADO.Net objects may be reinitialized and lose their values.

Persistence of Data between Page Postback We can store variables and ADO objects in Session or Application.

Increase Counter by One. What is wrong? Dim counter As Integer Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click counter = counter + 1 Response.Write(counter) End Sub

Save Counter in Session Dim counter As Integer Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click counter = counter + 1 Session("MyCounter") = counter Response.Write(counter) End Sub Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not Page.IsPostBack Then Session("MyCounter") = counter Else counter = Session("MyCounter") End If End Sub

Example: Save DataReader in Sesson Create a data reader Use button to display record one at a time

Dim strConn As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2007.accdb“ Dim objConn As New OleDbConnection(strConn) Dim strSQL As String = "select * from customer;" Dim objComm As New OleDbCommand(strSQL, objConn) Dim objDataReader As OleDbDataReader Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not Page.IsPostBack Then objConn.Open() objDataReader = objComm.ExecuteReader() objDataReader.Read() TextBox1.Text = objDataReader("cid") TextBox2.Text = objDataReader("cname") Session("myReader") = objDataReader Else objDataReader = Session("myreader") End If End Sub Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) If objDataReader.Read() = True Then TextBox1.Text = objDataReader("cid") TextBox2.Text = objDataReader("cname") Else Label1.Text = "no more record" objConn.Close() End If End Sub

DataSet Example Create a web form with a Radiobuttonlist to choose rating and display customers with the selected rating in a data grid. RadioButtonList control: –Items property –SelectedValue property

Data Binding with DataView And Save the Dataset in Session If Not Page.IsPostBack Then Response.Write(Session("CurrentDay")) Dim strConn As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2007.accdb“ Dim objConn As New OleDbConnection(strConn) Dim objDataSet As New DataSet() Dim strSQL As String = "select * from customer;" Dim objAdapter As New OleDbDataAdapter(strSQL, objConn) objAdapter.Fill(objDataSet, "Customer") Dim ObjDataView As New DataView() ObjDataView = objDataSet.Tables("Customer").DefaultView GridView1.DataSource = ObjDataView GridView1.DataBind() Session("DS") = objDataSet End If

Selecting a Subset of Records with DataView’s RowFilter Property objDataView.RowFilter = criteria Note: The criteria can be a simple or complex condition.

DataView Example Protected Sub RadioButtonList1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles RadioButtonList1.SelectedIndexChanged objDataSet = Session("DS") Dim ObjDataView As New DataView() ObjDataView.Table = objDataSet.Tables("Customer") ObjDataView.RowFilter = "rating='" & RadioButtonList1.SelectedValue & "'" GridView1.Visible = True GridView1.DataSource = ObjDataView GridView1.DataBind() End Sub

Binding a ListBox and Display Two Fields Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load If Not Page.IsPostBack Then Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQL As String = "select * from customer;" Dim objAdapter As New OleDbDataAdapter(strSQL, objConn) objAdapter.Fill(objdataset, "Customer") ListBox1.DataSource = objdataset.Tables("customer") ListBox1.DataTextField = "CID" ListBox1.DataValueField = "Cname" ListBox1.DataBind() Session("MyDataset") = objdataset Else objdataset = Session("MyDataset") End If End Sub Protected Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged TextBox1.Text = ListBox1.SelectedValue TextBox2.Text = objdataset.Tables("customer").Rows(ListBox1.SelectedIndex)("Rating") End Sub

DataTable’s Rows Property This is a collection of all the records in a table, a collection of DataRow objects. DataRow object’s properties and methods.

Accessing a Record with Index objAdapter.Fill(objDataSet, "Customer") TextBox1.Text = objDataSet.Tables("Customer").Rows(rowIndex).Item(0) TextBox2.Text = objDataSet.Tables("Customer").Rows(rowIndex).Item(1)

A page with CID Listbox to display customer data in textboxes and orders data in GridView. Use one adapter to create a dataset with two tables. Create bound listbox and automatically select the first customer’s CID: – ListBox1.Items(0).Selected = True GridView control is bound using Orders table’s view.

Creating Multiple Tables: One Adapter, Many Tables Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQLCustomer As String = "select * from customer;" Dim strSQLOrders As String = "select * from orders" Dim objAdapter As New OleDbDataAdapter(strSQLCustomer, objConn) Dim objDataset As New DataSet objAdapter.Fill(objDataset, "Customer") objAdapter.SelectCommand.CommandText = strSQLOrders objAdapter.Fill(objDataset, "orders")

Bind GridView to Orders table’s View Dim ObjDataView As New DataView() ObjDataView = objDataset.Tables("Orders").DefaultView ObjDataView.RowFilter = "CID='" & ListBox1.SelectedValue & "'" GridView1.DataSource = ObjDataView GridView1.DataBind()

If Not Page.IsPostBack Then Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQLCustomer As String = "select * from customer;" Dim strSQLOrders As String = "select * from orders" Dim objAdapter As New OleDbDataAdapter(strSQLCustomer, objConn) objAdapter.Fill(objDataset, "Customer") objAdapter.SelectCommand.CommandText = strSQLOrders objAdapter.Fill(objDataset, "orders") ListBox1.DataSource = objDataset.Tables("customer") ListBox1.DataTextField = "CID" ListBox1.DataValueField = "CID" ListBox1.DataBind() ListBox1.Items(0).Selected = True TextBox1.Text = objDataset.Tables("customer").Rows(ListBox1.SelectedIndex)("Cname") TextBox2.Text = objDataset.Tables("customer").Rows(ListBox1.SelectedIndex)("Rating") Dim ObjDataView As New DataView() ObjDataView = objDataset.Tables("Orders").DefaultView ObjDataView.RowFilter = "CID='" & ListBox1.SelectedValue & "'" GridView1.DataSource = ObjDataView GridView1.DataBind() Session("DS") = objDataset End If

Listbox’s SelectedIndexChanged Event Protected Sub ListBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged objDataset = Session("DS") TextBox1.Text = objDataset.Tables("customer").Rows(ListBox1.SelectedIndex)("Cname") TextBox2.Text = objDataset.Tables("customer").Rows(ListBox1.SelectedIndex)("Rating") Dim ObjDataView As New DataView() ObjDataView = objDataset.Tables("Orders").DefaultView ObjDataView.RowFilter = "CID='" & ListBox1.SelectedValue & "'" GridView1.DataSource = ObjDataView GridView1.DataBind() Session("DS") = objDataset End Sub

Share Variables between Pages First page: –Session("CustomerName") = objDataReader("cname") Second page: – Response.Write("Welcome, " + Session("CustomerName"))

Working with Session Start Event in Global.ASAX In Global.ASAX – Public CurrentDay As String – Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs) – CurrentDay = "Today is " + Now().DayOfWeek.ToString + ", " + Now().ToString – Session("CurrentDay") = CurrentDay –End Sub In a web page: –Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load – response.Write(session("CurrentDay")) –End Sub