Introduction
SqlConnection and SqlCommand are classes of a
connected architecture and found in the System.Data.SqlClient namespace. The SqlConnection
class makes the connection with the database. Further this connection (database
connection) is used by the SqlCommand to work with that database. The SqlCommand class
is used to execute the SQL statements. Let's work with the SqlConnection and SqlCommand
classes with simple examples.
SqlConnection Class
Here, we will use two important methods of SqlConnection.
Open() : The open() method is used to open the Database
connection.
Close() : The close() method is used to close the Database
connection.
Look at the following code:
using System;
using
System.Data;
using
System.Data.SqlClient;
namespace
sqlconnectionANDsqlcommand
{
public partial
class Form1 :
Form
{
public Form1()
{
InitializeComponent();
}
private void
btnclick_Click(object sender,
EventArgs e)
{
SqlConnection conn =
new SqlConnection("Database=student;Server=.;user=sa;password=aaaaaaa");
conn.Open();
// Open the
connection
// body
// body
conn.Close();
// Close the
connection
}
}
}
In the preceding code, I have added the namespace "System.Data.SqlClient". On the button
click event, I have created an
instance as "conn" of
SqlConnection and passing a connection string (database) as parameter. Then, I
have opened the connection by the open() method and closed to it by the close() method.
We can also check whether the connection is open or closed by it's state
property.
Add the following code to the application.
private
void btnclick_Click(object
sender, EventArgs e)
{
// connection is opened. so if you click
button then messagebox will be shown with the message "Open"
SqlConnection conn =
new SqlConnection("Database=student;Server=.;user=sa;password=aaaaaaa");
conn.Open();
MessageBox.Show(conn.State.ToString());
conn.Close();
}
private void
btnok_Click(object sender,
EventArgs e)
{
// connection is not opened. so if you
click button then messagebox will be shown with the message "Closed"
SqlConnection conn =
new SqlConnection("Database=student;Server=.;user=sa;password=aaaaaaa");
MessageBox.Show(conn.State.ToString());
}
SqlCommand Class
The main role of SqlCommand is to execute SQL statements.
Properties
CommandText: The commandText property is used to set the SQL statement.
Connection: This property is used to get connection to the database
source which is specified in SqlConnection.
Method
ExecuteNonQuery() : The
ExecuteNonQuery() method does not return any record. Which means we use
ExecuteNonQuery() in all operations with databases except retrieving records from a
database. It only returns the number of affected rows.
Now we use this method in our application. There is a database "student" and a
database "student_detail" which has no record. I am giving a simple example to
insert a record into database.
Take 3 labels, 3 textboxes and 1 button and arrange them as in the following figure.
![sqlconnection class in .net]()
Write the following code
using System;
using
System.Collections.Generic;
using
System.ComponentModel;
using
System.Data;
using
System.Drawing;
using
System.Linq;
using
System.Text;
using
System.Windows.Forms;
using
System.Data.SqlClient;
namespace
sqlconnectionANDsqlcommand
{
public partial
class Form1 :
Form
{
public Form1()
{
InitializeComponent();
}
private void
Form1_Load(object sender,
EventArgs e)
{
}
private void
btnclick_Click(object sender,
EventArgs e)
{
// Creating instance of SqlConnection
SqlConnection conn =
new SqlConnection("Database=student;Server=.;user=sa;password=aaaaaaa");
conn.Open();// open the database
connection
SqlCommand cmd =
new SqlCommand();//
Creating instance of SqlCommand
cmd.Connection = conn; // set the
connection to instance of SqlCommand
cmd.CommandText = "insert into
student_detail values (" + txtrollno.Text + ",'" + txtname.Text + "','" +
txtcourse.Text + "')";
// set
//the sql command ( Statement )
cmd.ExecuteNonQuery();
MessageBox.Show("Record
Saved"); // showing messagebox for confirmation
message for user
conn.Close();// Close the
connection
}
}
}
Output
Enter the RollNo., Name and Course and click the "save" button. It will save
the record into database.
ExecuteScalar() : The
ExecuteScalar() returns a single value from the database. Generally it is used with an
aggregate function (a function which returns a single value).
Suppose there is a need to check how many records are in the database table. Then we use
this function. Add another button to your application and set its text property
to "Count" and write the following code on button click.
private
void btncount_Click(object
sender, EventArgs e)
{
SqlConnection conn =
new SqlConnection("Database=student;Server=.;user=sa;password=aaaaaaa");
conn.Open();// open the database
connection
SqlCommand cmd =
new SqlCommand();//
Creating instance of SqlCommand
cmd.Connection = conn; // set the
connection to instance of SqlCommand
cmd.CommandText = "select count
(*) from student_detail" ; // set the sql
command ( Statement )
string record= cmd.ExecuteScalar().ToString();
MessageBox.Show("Total
records : "+ record );
conn.Close();// Close the connection
}
Output
When you click the "count" button, a MessageBox will be displayed to show the
total number of records in the database table.
ExecuteReader() : The
ExecuteReader() method can return a set of records from a database.
I will explain more about the ExecuteReader() method in my next article....
Here are some related resources.