Coding ADO.NET Objects:Connection, Command, DataReader
A Simplified View of ADO.NetObjects
Ado.Net
Data Provider
Connection
Adapter
Command
Reader
Dataset
Data Consumer
WinForm
WebForm
SQL Updates
Results of SQL Selects
Import NameSpace
•For MS Access accdb:
–using System.Data.OleDb;
•For SQL Express:
–using System.Data.SqlClient;
Connection Object
•A connection object represents a unique sessionwith 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 aconnection.
Connection String
•Containing information about database, OLE DBprovider, 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;IntegratedSecurity=True“
•For SQL Server Express LocalDB
–Data Source=(localdb)\projects;Initial Catalog=SalesDB;Integrated Security=True
Define Connection Object
•Example 1 – Access accdb:
– string strConn = "Provider=Microsoft.ACE.OLEDB.12.0;DataSource=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;IntegratedSecurity=True";
–SqlConnection objConn = new SqlConnection(strConn);
–objConn.Open();
•Basic Methods:
–Open, Close
–BeginTransaction
•Note: The “\\” is very important
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 resultsof the query.
–ExecuteScalar: Executes the query, and returns the first column of thefirst row in the result set returned by the query. Typically used toexecute a SQL aggregate function such as SUM, MAX, MIN, etc.
–ExecuteNonQuery: Change the data in a database without using aDataSet by executing SQL’s UPDATE, INSERT, or DELETEstatements.
DataReader Object
•It is read-only and forward-only cursor.
•Basic Methods:
–Read: Reads the current record and advances thepointer to the next record. It returns False if no morerecord in the DataReader.
–Close: Closes the dataReader.
•Property:
–HasRows – Boolean, indicates whether thisSystem.Data.Common.DbDataReader contains one ormore rows.
ExecuteReader Example
string strConn = "Data Source=(localdb)\\projects;InitialCatalog=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");
}
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 indicateif more records exist.
•To read a field:
–DataReader[“field name’].ToString();
–or
–DataReader[field index].ToString();
Example: Display One Record at a Time
Form Load Event
SqlDataReader objDataReader;
private void Form5_Load(object sender, EventArgs e)
{
string strConn = "Data Source=(localdb)\\projects;InitialCatalog=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");
}
}
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");
}
Use Loop to Read Records in aDataReader
• string Results="";
• while (objDataReader.Read()==true)
• {
• Results+=objDataReader["cid"] + " " +objDataReader["Cname"] + Environment.NewLine;
• }
•textBox1.Text = Results.ToString();
DataReader Example
string strConn = "Data Source=(localdb)\\projects;InitialCatalog=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();
Using Field Index
string strConn = "Data Source=(localdb)\\projects;InitialCatalog=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();
Add Items from a DataReader to a Listbox
string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;IntegratedSecurity=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
Display Selected Customer Info in Textbox
private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
{
string strConn = "Data Source=(localdb)\\projects;InitialCatalog=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();
}
Using a Parallel ArrayList toStore Cname and Rating
•ArrayList
–Add
–Clear
–Remove
–IndexOf
•Must add this reference:
–using System.Collections;
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;InitialCatalog=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"]);
}
}
Use Listbox SelectedIndex
private void listBox1_SelectedIndexChanged(object sender,EventArgs e)
{
textBox1.Text =CnameList[listBox1.SelectedIndex].ToString();
textBox2.Text =RatingList[listBox1.SelectedIndex].ToString();
}
Use SQL to Retrieve Summaries
string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;IntegratedSecurity=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
Using Command’s ExecuteScalar toRun SQL Aggregates
string strConn = "Data Source=(localdb)\\projects;InitialCatalog=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();
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;InitialCatalog=SalesDB;Integrated Security=True";
SqlConnection objConn = new SqlConnection(strConn);
objConn.Open();
SqlCommand objComm = new SqlCommand(strSQL, objConn);
textBox1.Text = objComm.ExecuteScalar().ToString();
objConn.Close(); }
Testing for Null:DBNull.Value
if ( objDataReader["rating"]==DBNull.Value)
{
textBox2.Text = "NA";
}
else
{
textBox2.Text = objDataReader["rating"].ToString();
}
Display Records with DataGridView
string strConn = "Data Source=(localdb)\\projects;Initial Catalog=SalesDB;IntegratedSecurity=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();
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?
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.
Working with ODBC DataSource
•Enter: using System.Data.Odbc;
•Use:
–OdbcConnection: Use DSN
•Example of connection string:
– string strConn = "DSN=SalesDBDSN";
–OdbcCommand
–OdbcDataReader
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();
}