1. Coding ADO.NET Objects: Connection, Command, DataReader

2. A Simplified View of ADO.Net Objects Ado.Net Data Provider Connection Adapter Command Reader Dataset Data Consumer WinForm WebForm SQL Updates Results of SQL Selects

3. Connection with a Connection Object A connection object represents a unique session with a data source. Property: –Connection string: string used to open a database. Data source, OLE DB provider, password, if any, security, etc. Methods: –Use the Open/Close method to open/close a connection.

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:\salesDB.mdb“ For Access 2007, 2011: –= "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\SalesDB2011.accdb“ For SQL Server Express –"Data Source=David-PC\sqlexpress;Initial Catalog=testSQL08;Integrated Security=True“ For SQL Server Express LocalDB –Data Source=(localdb)\v11.0;Initial Catalog=MyDept2;Integrated Security=True

5. Connection Object Example 1 – Jet Database: –string strConn ="Provider=Microsoft.Jet.OLEDB.4.0;Data Source = c:\\salesDB.mdb"; – OleDbConnection objConn = new OleDbConnection(strConn); –objConn.Open(); Example 2 – Access 2011: – string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; –OleDbConnection objConn = new OleDbConnection(strConn); –objConn.Open(); Object Browser: System.Data.OleDB/oledbConnection/New Basic Methods: –Open, Close –BeginTransaction

6. 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. –ExecuteScalar: Executes the query, and returns the first column of the first row in the result set returned by the query. Typically used to execute a SQL aggregate function such as SUM, MAX, MIN, etc. –ExecuteNonQuery: Change the data in a database without using a DataSet by executing SQL’s UPDATE, INSERT, or DELETE statements.

7. 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. Property: –HasRows – Boolean, indicates whether this System.Data.Common.DbDataReader contains one or more rows.

8. ExecuteReader Example string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL,objConn); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); if (objDataReader.HasRows) { MessageBox.Show("Data reader contains rows"); } else { MessageBox.Show("No row reurns"); }

9. Import NameSpace The “using” statement must appear before all other declarations in a file and cannot appear inside a class or module declaration. –using System.Data.OleDb;

10. Read a Record in a DataReader DataReader’s Read method: –The Read method will (1) read a record, (2) advance pointer, (3) return true/false to indicate if more records exist. To read a field: –DataReader[“field name’].ToString(); –or –DataReader[field index].ToString();

11. Example: Display One Record at a Time

12. Form Load Event OleDbDataReader objDataReader; private void Form2_Load(object sender, EventArgs e) { string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Csharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); // OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); if (objDataReader.HasRows) { MessageBox.Show("Data reader contains rows"); objDataReader.Read(); textBox1.Text = objDataReader["CID"].ToString(); textBox2.Text = objDataReader["Cname"].ToString(); } else { MessageBox.Show("No row reurns"); }

13. Button Event private void button1_Click(object sender, EventArgs e) { if (objDataReader.Read()) { textBox1.Text = objDataReader["CID"].ToString(); textBox2.Text = objDataReader["Cname"].ToString(); } else MessageBox.Show("No more data"); }

14. Read Records in a DataReader string Results=""; while (objDataReader.Read()==true) { Results+=objDataReader["cid"] + " " + objDataReader["Cname"] + Environment.NewLine; } textBox1.Text = Results.ToString();

15. DataReader Example string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL,objConn); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); string Results=""; while (objDataReader.Read()==true) { Results += objDataReader["cid"] + " " + objDataReader["Cname"] + Environment.NewLine; } textBox1.Text = Results.ToString();

16. Using Field Index string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); string Results = ""; while (objDataReader.Read() == true) { Results += objDataReader[0] + " " + objDataReader[1] + Environment.NewLine; } textBox1.Text = Results.ToString();

17. Add Items from a DataReader to a Listbox string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select cid from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); OleDbDataReader objDataReader; objDataReader=objComm.ExecuteReader(); while (objDataReader.Read()==true) { listBox1.Items.Add(objDataReader["cid"]); // listBox1.Items.Add(objDataReader.GetString(0)); } Note1: Listbox is not bound. 2. SelectedItem

18. Display Selected Customer Info in Textbox private void listBox1_SelectedIndexChanged(object sender, EventArgs e) { string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select * from customer where cid='" + listBox1.SelectedItem + "'"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); objDataReader.Read(); textBox1.Text = objDataReader["Cname"].ToString(); textBox2.Text = objDataReader["rating"].ToString(); objConn.Close(); }

19. Using a Parallel ArrayList to Store Cname and Rating ArrayList –Add –Clear –Remove –IndexOf Must add this reference: –using System.Collections;

20. Using a Parallel ArrayList ArrayList CnameList = new ArrayList(),RatingList = new ArrayList(); private void Form1_Load(object sender, EventArgs e) { string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select * from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); while (objDataReader.Read() == true) { listBox1.Items.Add(objDataReader["cid"]); CnameList.Add(objDataReader["cname"]); RatingList.Add(objDataReader["rating"]); } objConn.Close(); }

21. Use Listbox SelectedIndex private void listBox1_SelectedIndexChanged(object sender, EventArgs e) { textBox1.Text = CnameList[listBox1.SelectedIndex].ToString(); textBox2.Text = RatingList[listBox1.SelectedIndex].ToString(); }

22. Use SQL to Retrieve Summaries string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select count(cid) as custCount from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); if (objDataReader.Read() == true) { MessageBox.Show(objDataReader["custCount"].ToString()); } objConn.Close(); Note: Alias ----- select count(cid) as custCount

23. Using Command’s ExecuteScalar to Run SQL Aggregates string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select count(cid) as custCount from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); textBox1.Text = objComm.ExecuteScalar().ToString(); objConn.Close();

24. ExecuteScalar Example private void radioButton_CheckedChanged(object sender, EventArgs e) { string strSQL; if (radioButton1.Checked) { strSQL = "select count(pid) as prodCount from product;"; } else if (radioButton2.Checked) { strSQL = "select max(price) as maxPrice from product;"; } else { strSQL = "select min(price) as minPrice from product;"; } string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); textBox1.Text = objComm.ExecuteScalar().ToString(); objConn.Close(); }

25. Testing for Null: DBNull.Value if ( objDataReader["rating"]==DBNull.Value) { textBox2.Text = "NA"; } else { textBox2.Text = objDataReader["rating"].ToString(); }

26. Error Handling string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select cid from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); try { objConn.Open(); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); while (objDataReader.Read() == true) { listBox1.Items.Add(objDataReader["cid"]); } catch (System.Exception ex) { MessageBox.Show(ex.Message); } objConn.Close(); Note: Where do declare objConn?

27. Possible Database Errors SQL syntax errors Database connection not open Null Violate database constraints Referential integrity Field data type and length Primary key constraint Invalid data – database may have validation rules.

28. Working with ODBC Data Source Enter: using System.Data.Odbc; Use: –OdbcConnection: Use DSN Example of connection string: – string strConn = "DSN=test32SQLDS"; –OdbcCommand –OdbcDataReader

29. using System.Data.Odbc; private void Form5_Load(object sender, EventArgs e) { string strConn = "DSN=test32SQLDS"; OdbcConnection objConn = new OdbcConnection(strConn); string strSQL = "select cid from customer;"; OdbcCommand objComm = new OdbcCommand(strSQL, objConn); try { objConn.Open(); OdbcDataReader objDataReader; objDataReader = objComm.ExecuteReader(); while (objDataReader.Read() == true) { listBox1.Items.Add(objDataReader["cid"]); } catch (System.Exception ex) { MessageBox.Show(ex.Message); } objConn.Close(); }

30. Working with SQL Server Database Enter: using System.Data.SqlClient; Use: –SqlConnection: –Example of connection string: – string strConn = "Data Source=David- PC\\SQLEXPRESS;Initial Catalog=TestSQLServer;Integrated Security=True;Pooling=False"; –SqlCommand –SqlDataReader

31. Working with SQL Server Data Source private void Form5_Load(object sender, EventArgs e) { string strConn = "Data Source=David-PC\\SQLEXPRESS;Initial Catalog=TestSQLServer;Integrated Security=True;Pooling=False"; SqlConnection objConn = new SqlConnection(strConn); string strSQL = "select cid from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); try { objConn.Open(); SqlDataReader objDataReader; objDataReader = objComm.ExecuteReader(); while (objDataReader.Read() == true) { listBox1.Items.Add(objDataReader["cid"]); } catch (System.Exception ex) { MessageBox.Show(ex.Message); } objConn.Close(); }

32. Working with SQL Server LocalDB Connection string example: Connecting to MyDept database: –string strConn = "Data Source=(localdb)\\v11.0;Initial Catalog=MyDept;Integrated Security=True"; Note: (localdb)\\v11.0 –The “\\” is very important

33. Display Records with DataGridView string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; OleDbConnection objConn = new OleDbConnection(strConn); string strSQL = "select * from customer;"; OleDbCommand objComm = new OleDbCommand(strSQL, objConn); objConn.Open(); OleDbDataReader objDataReader; objDataReader = objComm.ExecuteReader(); dataGridView1.ColumnCount = 4; dataGridView1.Columns[0].HeaderText = "CID"; dataGridView1.Columns[1].HeaderText = "Cname"; dataGridView1.Columns[2].HeaderText = "City"; dataGridView1.Columns[3].HeaderText = "Rating"; dataGridView1.Rows.Clear(); int rowIndex = 0; while (objDataReader.Read() == true) { dataGridView1.Rows.Add(); dataGridView1.Rows[rowIndex].Cells[0].Value = objDataReader["cid"]; dataGridView1.Rows[rowIndex].Cells[1].Value = objDataReader["cname"]; dataGridView1.Rows[rowIndex].Cells[2].Value = objDataReader["city"]; dataGridView1.Rows[rowIndex].Cells[3].Value = objDataReader["rating"]; rowIndex += 1; } objConn.Close();