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:– <asp:datagrid id="dgCustomer" runat="server"
/><br />
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("cid"))
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+"<b>" & objRow("cid")
& " " & objRow("cname") & "</b><br />"
• 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?
<script runat="server">
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 SessionDemo: StateTestCounter2.ASPX
<script runat="server">
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=strConnstrSQL = "select * from customer;"dim objAdapter as new OledbDataAdapter(strSQL, objConn)objAdapter.Fill(objDataSet, "Cust")objDataView=objDataSet.Tables("cust").DefaultViewdgCustomer.Datasource=objDataViewdgCustomer.DataBind()response.write ("this is the first grid")Session("MyDataSet")=objDataSet
end ifend sub
sub ClickHandler(Sender As Object, E As EventArgs)objDataSet=Session("MyDataSet")objDataView=objDataSet.tables("Cust").defaultViewdgCustomer2.Datasource=objDataViewdgCustomer2.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 ObjectsDim 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