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. Import NameSpace For MS Access accdb: –using System.Data.OleDb; For SQL Express: –using System.Data.SqlClient;

4. 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.

5. Connection String Containing information about database, OLE DB provider, password, if any, security, etc. For ODBC DSN: SalesDB –=“DSN=SalesDBDSN“ For Access 2011, 2013: –= "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)\projects;Initial Catalog=SalesDB;Integrated Security=True

6. Define Connection Object Example 1 – Access accdb: – string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\CSharpexamples\\SalesDB2011.accdb"; –OleDbConnection objConn = new OleDbConnection(strConn); –objConn.Open(); Example 2 – SQL Express LocalDB –string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; –SqlConnection objConn = new SqlConnection(strConn); –objConn.Open(); Basic Methods: –Open, Close –BeginTransaction Note: The “\\” is very important

7. 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.

8. 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.

9. ExecuteReader Example string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader objDataReader; objDataReader = objComm.ExecuteReader(); if (objDataReader.HasRows) { MessageBox.Show("Data reader contains rows"); } else { MessageBox.Show("No row reurns"); }

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 SqlDataReader objDataReader; private void Form5_Load(object sender, EventArgs e) { string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); // SqlDataReader 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. Use Loop to 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer where cid='" + listBox1.SelectedItem + "'"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader 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 Form5_Load(object sender, EventArgs e) { string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader objDataReader; objDataReader = objComm.ExecuteReader(); while (objDataReader.Read() == true) { listBox1.Items.Add(objDataReader["cid"]); CnameList.Add(objDataReader["cname"]); RatingList.Add(objDataReader["rating"]); }

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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select count(cid) as custCount from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select count(cid) as custCount from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); SqlCommand objComm = new SqlCommand(strSQL, objConn); 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. Display Records with DataGridView string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); objConn.Open(); string strSQL = "select * from customer;"; SqlCommand objComm = new SqlCommand(strSQL, objConn); SqlDataReader 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();

27. Error Handling: Try/Catch 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 = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;Integrated Security=True"; SqlConnection objConn = new SqlConnection(strConn); try { objConn.Open(); SqlCommand objComm = new SqlCommand(strSQL, objConn); textBox1.Text = objComm.ExecuteScalar().ToString(); objConn.Close(); } catch (System.Exception ex) { MessageBox.Show(ex.Message); } Note: Where do declare objConn?

28. 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.

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

30. using System.Data.Odbc; private void Form5_Load(object sender, EventArgs e) { string strConn = "DSN=SalesDBDSN"; 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(); }