ASP.NET and ADO.NET

ADO.NET Objects Data Set.NET Applications Data Reader Command Object Connection Object Managed Data Provider (OLEDB) Database

Bind the DataReader to a Server Control DataGrid: –dim objDataReader as oledbDataReader –objDataReader=objComm.executeReader() –dgCustomer.datasource=objDataReader –dgCustomer.DataBind() The Datagrid is defined as: – Demo: CommandReadCust.ASPX

Select Rating from a RadiobuttonList Private Sub RadioButtonList1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButtonList1.SelectedIndexChanged Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQL As String = "select * from customer where rating = '" & RadioButtonList1.SelectedItem.Value & "'" Dim objComm As New OleDbCommand(strSQL, objConn) Dim Results As String objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() DataGrid1.DataSource = objDataReader DataGrid1.DataBind() End Sub

ListControl Base Class DropDownList, ListBox, CheckBoxList, RadioButtonList Properties: –AutoPostBack –DataSource –DataTextField: The field in the datasource that provides the text to be used for the list items. –DataValueField –SelectedItem Note: Value of the selected item: SelectedItem.Value Event: OnSelectedIndexChanged

Some Possible Causes of Error The procedure in the Page_Load event is executed everytime the web page is loaded. –1. The AutoPostBack property must set to True for the OnSelectedIndexChanged event to work. –2. If the ListItems are created by the Items.Add method, it may be duplicated. –3. The ADO.Net objects and binding do not need to be recreated every time. If not page.isPostBack then … Demo: ASPNET/ListBoxPostback.aspx

Binding a DataReader to a DropDownList with PostBack Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load If Not Page.IsPostBack Then Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQL As String = "select cid from customer;" Dim objComm As New OleDbCommand(strSQL, objConn) objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() ListBox1.DataSource = objDataReader ListBox1.DataTextField = "CID" ListBox1.DataBind() End If End Sub Note: ListBox PostBack property is set to True.

Display Selected Customer in dataGrid Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQL As String = "select * from customer where cid = '" & ListBox1.SelectedItem.Value & "'" Dim objComm As New OleDbCommand(strSQL, objConn) objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() DataGrid1.DataSource = objDataReader DataGrid1.DataBind() End Sub

Use List Items’ Add Method to Create a DropDownList from a DataReader do while objDataReader.Read()=true Cnamelist.items.add (objDataReader("Cname")) loop

Demo:ReaderUpdate.Aspx Use a DataReader to create a dropwdownList with customer names.. Use a second DataReader to bind the selected customer data to a datagrid. Let user to choose a new customer rating from a listbox. Update customer’s rating using Command object’s ExecuteNonQuery method. Create another reader to bind the selected customer’s new data in a second grid.

DataSet and Related Objects DataSet: Can contain multiple tables and relationships. DataTable object: Represents a table in the dataset. DataAdapter: This the object used to pass data between the database and the dataset. The Fill method copies the data into the dataset, and the Update method copies the updates back into the database. DataView: This represents a specific view of the DataTables held in the dataset.

Reading Data into a Table dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" dim objConn as new OledbConnection(strConn) dim strSQL as string = "select * from customer;" dim objDataSet as new Dataset() dim objAdapter as new OledbDataAdapter(strSQL, objConn) objAdapter.Fill(objDataSet, "Cust")

Binding a Table to a Server Control Each Table object has a DefaultView property. Create a DataView object for the table, then use the DataView object to bind the control. objAdapter.Fill(objDataSet, "Cust") dim objDataView as new DataView(objDataSet.tables("Cust")) dgCustomer.Datasource=objDataView dgCustomer.DataBind() Demo: AdapterReadCust.Aspx

DataView Object The DataView object exposes a complete table or a subset of the records from a table. Properties: –RowFilter –objDataView.rowfilter="rating='" & Ratinglist.SelectedItem.Text & "'“ –Demo: AdapterReadcustView.aspx, AdapterReadcustView2.aspx –AdapterReadcustView3.aspx

Creating Multiple Tables in A DataSet dim strSQLCust as string = "select * from customer;" dim strSQLOrder as string ="select * from orders;" dim objComm as new OledbCommand() dim objAdapter as new OledbDataAdapter() dim objDataSet as new Dataset() objComm.Connection=objConn objComm.CommandType=COmmandType.Text objComm.CommandText=strSQLCust objAdapter.SelectCommand=objComm objConn.open() objAdapter.Fill(objDataSet, "Customer") objComm.COmmandText=strSQLOrder objAdapter.Fill(objDataSet, "Orders") Demo: AdapterCustOrder.aspx

Adding Relationship to a Dataset The Dataset object has a Relations property. It is a collection of DataRelations. We can use a relationship to enforce the referential integrity. To define a DataRelation: –DataRelObj=DataRelation(RelationName, ParentTable Field, ChildTableField) objRel = New DataRelation("custOrder", objDataset.tables("customer").columns(" cid"), objDataset.tables("orders").columns("ci d"))

DataTable’s Rows Property This is a collection of all the records in a table, a collection of DataRow objects. The DataRow object has a GetChildRows method that returns a collection of rows from another table that are related as child rows to this row.

Access Rows in a DataRow Collection dim objTable as DataTable = objDataset.Tables("Customer") dim objRow as DataRow For each objRow in objTable.Rows strResult=strResult+" " & objRow("cid") & " " & objRow("cname") & " " Next

Displaying Parent/Child Records in a Relation Define the relation. Specify the relation in the GetChildRows method of the DataRow object. Demo: ParentChild.Aspx, ParentChildTable.aspx

Persistence of Data between Page Postback Each page is entirely new each time we submit information to the same page. There is no persistence of information between pages (other than the ViewState which remembers the data contained in controls). Variables and ADO objects are lost. We can store variables and ADO objects in Session or Application. Demo: StateTestCounter.ASPX, PersistDataSet.Aspx

Increase Counter by One. What is wrong? dim counter as integer sub Page_Load() counter=0 end sub sub IncreaseCounter(sender as object, e as EventArgs) counter=counter+1 response.write("The counter's value is:" + cstr(counter)) end sub Demo: StateTestCounter.ASPX

Save Counter in Session Demo: StateTestCounter2.ASPX dim counter as integer sub Page_Load() if not page.isPostBack then counter=0 session("MyCounter")=counter else counter=session("MyCounter") end if end sub sub IncreaseCounter(sender as object, e as EventArgs) counter=counter+1 response.write("The counter's value is:" + cstr(counter)) session("MyCounter")=counter End sub

sub Page_load() if not page.ispostback then strConn ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" objConn.connectionString=strConn strSQL = "select * from customer;" dim objAdapter as new OledbDataAdapter(strSQL, objConn) objAdapter.Fill(objDataSet, "Cust") objDataView=objDataSet.Tables("cust").DefaultView dgCustomer.Datasource=objDataView dgCustomer.DataBind() response.write ("this is the first grid") Session("MyDataSet")=objDataSet end if end sub sub ClickHandler(Sender As Object, E As EventArgs) objDataSet=Session("MyDataSet") objDataView=objDataSet.tables("Cust").defaultView dgCustomer2.Datasource=objDataView dgCustomer2.DataBind() response.write("this is ClcikHandler") end sub

The Effects of PostBack on Bound Controls If the databinding is done in a PageLoad event procedure without checking postback, the databinding is repeated and the control is initialized to its original state. For list controls, such as ListBox, CheckboxList, and Radiobuttonlist, the selected item is no longer selected.

Demo Dim fruits As New ArrayList() Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 'If Not Page.IsPostBack Then fruits.Add("apple") fruits.Add("orange") fruits.Add("banana") CheckBoxList1.DataSource = fruits CheckBoxList1.DataBind() 'End If End Sub Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click Dim i As Integer For i = 0 To CheckBoxList1.Items.Count - 1 If CheckBoxList1.Items(i).Selected Then Response.Write("you check" & CheckBoxList1.Items(i).Text) End If Next End Sub

Binding to an ArrayList (Collection) of Objects Dim emps As New ArrayList() Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load If Not Page.IsPostBack Then Dim myEMp1 As New Emp() myEMp1.eid = "e1" myEMp1.ename = "peter" myEMp1.salary = 5000 Dim myEmp2 As New Emp() myEmp2.eid = "e2" myEmp2.ename = "paul" myEmp2.salary = 6000 emps.Add(myEMp1) emps.Add(myEmp2) RadioButtonList1.DataSource = emps RadioButtonList1.DataTextField = "eid" RadioButtonList1.DataValueField = "salary" RadioButtonList1.DataBind() Session("MyEmps") = emps End If End Sub Private Sub RadioButtonList1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButtonList1.SelectedIndexChanged emps = Session("MyEmps") Response.Write(emps.Item(RadioButtonList1.SelectedIndex).ename) Response.Write(emps.Item(RadioButtonList1.SelectedIndex).salary.ToString) End Sub