penyaskito#

This is a simple guide for reading data from a database. I chose Access for the example, but using another Database Manager is very similar to this.

At first, we have to connect to the database, using its connection string, and open the connection:

OleDbConnection con;
con = new OleDbConnection();
con.ConnectionString = @�Provider=Microsoft.Jet.OLEDB.4.0;� +
@�Data source= C:\cd.mdb�;
con.Open();

Now we create the command. For this we use OleDbCommand. Its constructor receives as parameters one string with the SQL sentence and the connection object.

OleDbCommand cmd;
cmd = new OleDbCommand(“select * from Customers”, con);

For sentences that read data, we have to use the method ExecuteReader. Its result rows are saved in an object called DataReader.

OleDbDataReader dr;
dr = cmd.ExecuteReader();

Now we iterate over the reader and print data at console. For this we use a DataReader indexer, which parameter is the name of the column.

while (dr.Read())
{

Console.WriteLine(“Name: ” + dr["Name"].ToString();
Console.WriteLine(“Name: ” + dr["Phone"].ToString();
Console.WriteLine(“Name: ” + dr["Mail"].ToString();

}

Closing all opened connections is very important:

con.Close();

Writing good code is important. For writing good code, we should take care about exceptions methods can throw. In this little demo we don’t make it, but be careful in your applications.