Introduction to ADO.NET

1. Introduction to ADO.NET

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

3. Connection with a Connection Object • A connection object represents a unique session with a data source. • Connection string: database, OLE DB provider, password, if any, security, etc. • Use the Open/Close method to open/close a connection. • Other functions: • Manage transaction: BeginTransaction(), Commit, rollBack.

4. Connection String • Containing information about database, OLE DB provider, password, if any, security, etc. • For Jet database: • ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb"

5. Data Link Properties (Under the Advanced Tab of the Connection Dialog Window) • Access permissions • Read—Read only. • ReadWrite—Read and write. • Share Deny None—Neither read nor write access can be denied to others. • Share Deny Read—Prevents others from opening in read mode. • Share Deny Write—Prevents others from opening in write mode. • Share Exclusive—Prevents others from opening in read/write mode. • Write—Write only.

6. Providers • MSDASQL • Microsoft OLE DB Provider for ODBC • Microsoft.Jet.OLEDB.3.51 • Microsoft.Jet.OLEDB.4.0 • MSDAORA – For Oracle • SQLOLEDB – Microsoft SQL Server

7. Connection Object • Example 1: • dim strConn as string ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" • dim objConn as new OledbConnection(strConn) • objConn.open() • Example 2: • Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb;User ID=Admin;Password=" • Basic Methods: • Open, Close • BeginTransaction

8. Command Object • The command object allows us to execute a SQL statement. • Properties: • CommandType: Text, stored procedure, tableDirect • CommandText: SQL statement, procedure name, table name • Connection • Other properties: • Parameters • Basic Methods: • ExecuteReader: Creates a DataReader object that contains the results of the query. • ExecuteNonQuery: Change the data in a database without using a DataSet by executing SQL’s UPDATE, INSERT, or DELETE statements.

9. ExecuteReader Example 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 objComm as new OledbCommand(strSQL,objConn) dim Results as string objConn.open() dim objDataReader as oledbDataReader objDataReader=objComm.executeReader()

10. Import NameSpace • The Imports statement must appear before all other declarations in a file and cannot appear inside a class or module declaration. • Imports System.Data.OleDb • Public Class Form1 • Note: To import a nameSpace for all forms/modules in a project: • Use Project Property Page: Imports

11. DataReader Object • It is read-only and forward-only cursor. • Basic Methods: • Read: Reads the current record and advances the pointer to the next record. It returns False if no more record in the DataReader. • Close: Closes the dataReader.

12. Read Records in a DataReader • dim Results as string • do while objDataReader.Read()=true Results+=objDataReader("cid") + “ “ + objDataReader("Cname") + vbCrLF • loop • Textbox1.text=Results • Note: objDataReader.Item(0) • Note: objDataReader.Item(“cid”)

13. Add Items from a DataReader to a Listbox 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 cname from customer;" Dim objComm As New OleDbCommand(strSQL, objConn) objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() Do While objDataReader.Read() = True LISTBOX1.Items.Add(objDataReader("cname")) Loop Note1: Listbox is not bound. 2. SelectedItem Note2: With the data binding you cannot issue the Add method.

14. Use a DataReader to Retrieve Summaries Dim sfCount, laCount, aCount, bCount, cCOunt As Integer objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() Do While objDataReader.Read() = True If objDataReader("city") = "sf" Then sfCount += 1 ElseIf objDataReader("city") = "la" Then laCount += 1 End If If objDataReader("rating") = "a" Then aCount += 1 ElseIf objDataReader("rating") = "b" Then bCount += 1 Else cCOunt += 1 End If Loop TextBox1.Text = sfCount.ToString TextBox2.Text = laCount.ToString TextBox3.Text = aCount.ToString TextBox4.Text = bCount.ToString TextBox5.Text = cCOunt.ToString

15. Use SQL to Retrieve Summaries 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 count(cid) as custCount from customer;" Dim objComm As New OleDbCommand(strSQL, objConn) Dim Results As String objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() If objDataReader.Read = True Then MessageBox.Show(objDataReader("custCount").ToString) End If

16. Testing for Null If objDataReader.Read = True Then If IsDBNull(objDataReader("custCount")) Then TextBox1.Text = 0 Else TextBox1.Text = objDataReader("custCount").ToString End If End If Note: The keyword “Nothing” tests if an object is null.

17. Null Value Example 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 & "'" Dim objComm As New OleDbCommand(strSQL, objConn) objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() objDataReader.Read() TextBox1.Text = objDataReader("Cname") TextBox2.Text = objDataReader("rating") ‘ Statement won’t work if Rating is null in database End Sub

18. Setting a Field to Null with a Update Statement Dim strSQLUpd As String = "Update Customer Set Rating = null Where cid = '" & ListBox1.SelectedItem & "'"

19. To Reuse a DataReader • objDataReader.Close() • objDataReader = objComm.ExecuteReader()

20. Error Handling Try objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() Do While objDataReader.Read() = True Results += objDataReader("cid") + " " + objDataReader("Cname") + vbCrLf Loop TextBox1.Text = Results objConn.Close() Catch except As System.Exception MessageBox.Show(except.Message) End Try

21. Possible Database Errors • SQL syntax errors • Database connection not open • Null • Violate database constraints • Referential integrity • Field data type and length • Primary key constraint

22. ExecuteNonQuery Example dim strSQLUpd as string="Update customer set rating = ‘A’” strSQLUpd=strSQLUpd & " where cname='" & CnameList.selectedItem.text & "'“ Dim objCommUpd As New OleDbCommand(strSQLUpd, objConn) objCommUpd.ExecuteNonQuery() Note: How many records affected by this command? ExecuteNonQuery method returns an integer indicating the number of record affected by the update command. Messagebox.Show(objCommUpd.ExecuteNonQuery())

23. Demo • Create a project that do the following tasks: • Use a DataReader to retrieve customer IDs and populate a listbox. • Select a new rating from radio buttons for the selected customer. • Update customer’s rating using the ExecuteNonQuery method of a Command object.

24. Declare OleDB objects and create listbox Imports System.Data.OleDb Public Class Form3 Inherits System.Windows.Forms.Form 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) Private Sub Form3_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load objConn.Open() Dim objDataReader As OleDbDataReader objDataReader = objComm.ExecuteReader() Do While objDataReader.Read() = True ListBox1.Items.Add(objDataReader("cid")) Loop objConn.Close() End Sub

25. Update customer rating Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click objConn.Open() Dim newRating As String If RadioButton1.Checked = True Then newRating = "A" ElseIf RadioButton2.Checked Then newRating = "B" Else newRating = "C" End If Dim strSQLUpd As String = "Update customer set rating = '" & newRating & "'" strSQLUpd = strSQLUpd & " where cid='" & ListBox1.SelectedItem & "'" Dim objCommUpd As New OleDbCommand(strSQLUpd, objConn) objCommUpd.ExecuteNonQuery() objConn.Close() End Sub

26. Use Command Object’s ExecuteNonQuery to Insert A New Record • Create unbound text boxes to enter new record. • Add an Insert button with the following handler Dim strSQLInsert As String strSQLInsert = "Insert into Customer values ('" strSQLInsert = strSQLInsert & TextBox1.Text & "','" & TextBox2.Text & "','" strSQLInsert = strSQLInsert & TextBox3.Text & "','" & TextBox4.Text & "')" Dim objCommInsert As New OleDbCommand(strSQLInsert, objConn) objCommInsert.ExecuteNonQuery()

27. Transaction • OleDBTransaction • Dim objTrans As OleDbTransaction • objTrans= objConn.BeginTransaction() • objComm.Transaction = objTrans • Methods: Commit, RollBack • objTrans.Commit

28. DataSet Object • A DataSet object can hold several tables and relationships between tables. • A DataSet is a set of disconnedted data. Data is extracted from the database and stored in the DataSet object. Updates to the DataSet must copy back to the database to make the changes permanent.

29. 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.

30. DataSet and Related Objects DataSet Tables DataView DataAdapter Commands Connection DataSource

31. Structure of a Dataset Dataset Tables Data table Rows Data Row Columns Data Column Constraints Relations Constraint Data Relation

32. 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 strSQLSelect as string = "select * from customer;" • dim objDataSet as new Dataset() • dim objAdapter as new OledbDataAdapter(strSQLSelect, objConn) • objAdapter.Fill(objDataSet, "Cust")

33. Binding DataGrid with Code Imports System.Data.OleDb Public Class Form4 Inherits System.Windows.Forms.Form Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" Dim objConn As New OleDbConnection(strConn) Dim objDataSet As New DataSet() Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim strSQL As String = "select * from customer;" Dim objAdapter As New OleDbDataAdapter(strSQL, objConn) objAdapter.Fill(objDataSet, "Cust") DataGrid1.DataSource = objDataSet DataGrid1.DataMember = "Cust" End Sub Note: Adapter’s Fill method is able to open the connection.

34. Binding a ListBox with Code Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 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, "Customer") ListBox1.DataSource = objDataSet.Tables("Customer") ListBox1.DisplayMember = "CID" End Sub Private Sub ListBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBox1.SelectedIndexChanged TextBox1.Text = ListBox1.SelectedItem.item("cname") End Sub Note: The FieldName for the DisplayMember is case-sensitive and should match the field name in the database.

35. Binding Textbox with Code Private Sub Form4_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\salesDB.mdb" Dim objConn As New OleDbConnection(strConn) Dim strSQLSelect As String = "select * from customer;" 'Dim objAdapter As New OleDbDataAdapter(strSQLSelect, objConn) Dim objAdapter As New OleDbDataAdapter Dim objComm As New OleDbCommand(strSQLSelect, objConn) objAdapter.SelectCommand = objComm objAdapter.Fill(objDataSet, "Customer") txtCID.DataBindings.Add("text", objDataSet, "customer.cid") txtCname.DataBindings.Add("text", objDataSet, "customer.cname") txtCity.DataBindings.Add("text", objDataSet, "customer.city") txtRating.DataBindings.Add("text", objDataSet, "customer.rating") End Sub Private Sub btnNext_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnNext.Click Me.BindingContext(objDataSet, "customer").Position += 1 End Sub

36. DataView ObjectA Better Way for Binding • The DataView object exposes a complete table or a subset of the records from a table. • Table’s DefaultView property: • Dim ObjDataView As New DataView() • ObjDataView.Table = objDataSet.Tables("Cust") • Or: ObjDataView = objDataSet.Tables("Cust").DefaultView • DataView can be used as a DataSource in data binding.

37. Data Binding with DataView Object Dim strConn As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\sales2k.mdb" 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, "Cust") Dim ObjDataView As New DataView() ObjDataView = objDataSet.Tables("Cust").DefaultView DataGrid1.DataSource = ObjDataView

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

39. DataView Example Dim ObjDataView As New DataView() Dim newRating As String If RadioButton1.Checked = True Then newRating = "A" ElseIf RadioButton2.Checked Then newRating = "B" Else newRating = "C" End If ObjDataView.Table = objDataSet.Tables("Cust") ObjDataView.RowFilter = "rating='" & newRating & "'" DataGrid1.Visible = True DataGrid1.DataSource = ObjDataView

40. Accessing Records in DataView Using DataView and DataRowView object’s Item property: objdataView = objDataSet.Tables("customer").DefaultView TextBox1.Text = objdataView.Item(rowIndex).Item(0) TextBox2.Text = objdataView.Item(rowIndex).Item(1) Move to the next record: rowIndex += 1 TextBox1.Text = objdataView.Item(rowIndex).Item(0) TextBox2.Text = objdataView.Item(rowIndex).Item(1) Note: To avoid out-of-bound, use the DataView’s Count property.

41. Creating multiple tables: One Adapter, One Table 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 objAdapterCust As New OleDbDataAdapter(strSQLCustomer, objConn) Dim objAdapterOrd As New OleDbDataAdapter(strSQLOrders, objConn) Dim objDataset As New DataSet objAdapterCust.Fill(objDataset, "Customer") objAdapterOrd.Fill(objDataset, "orders")

42. 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") • DataGrid1.DataSource = objDataset

43. Binding Multiple Tables to a DataGrid (Example 1) DataGrid1.DataSource = objDataSet

44. Binding Multiple Tables to a DataGrid (Example 2) Dim ObjDataView As New DataView() Dim TableName As String If RadioButton1.Checked = True Then ObjDataView = objDataSet.Tables("Customer").DefaultView Else ObjDataView = objDataSet.Tables("Orders").DefaultView End If DataGrid1.DataSource = ObjDataView

45. 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) • Dim objRel As DataRelation • objRel = New DataRelation("custOrder", objDataset.tables("customer").columns("cid"), objDataset.tables("orders").columns("cid")) • Adding a relation to the dataset: • objDataSet.Relations.Add(objRel)

46. Creating a Hierarchical DataGrid Dim objRel As DataRelation objRel = New DataRelation("custOrder", objDataSet.Tables("customer").Columns("cid"), objDataSet.Tables("orders").Columns("cid")) objDataSet.Relations.Add(objRel) DataGrid1.DataSource = objDataSet.Tables("customer")

47. 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.

48. 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)

49. 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") & vbCrLf • Next

50. DataRow object’s GetChildRows Method • Returns a collection of rows from another table that are related as child rows to this row.