5.1.2 The MySqlCommand Object

Once a connection has been established with the MySQL database, the next step is do carry out the desired database operations. This can be achieved through the use of the MySqlCommand object.

You will see how to create a MySqlCommand object. Once it has been created, there are three main methods of interest that you can call:

Once a MySqlCommand object has been created, you will call one of the above methods on it to carry out a database operation, such as perform a query. The results are usually returned into a MySqlDataReader object, and then processed, for example the results might be displayed. The following code demonstrates how this could be done.

using System;
using System.Data;

using MySql.Data;
using MySql.Data.MySqlClient;

public class Tutorial2
{
    public static void Main()
    {
        string connStr = "server=localhost;user=root;database=world;port=3306;password=******;";
        MySqlConnection conn = new MySqlConnection(connStr);
        try
        {
            Console.WriteLine("Connecting to MySQL...");
            conn.Open();

            string sql = "SELECT Name, HeadOfState FROM Country WHERE Continent='Oceania'";
            MySqlCommand cmd = new MySqlCommand(sql, conn);
            MySqlDataReader rdr = cmd.ExecuteReader();

            while (rdr.Read())
            {
                Console.WriteLine(rdr[0]+" -- "+rdr[1]);
            }
            rdr.Close();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

        conn.Close();
        Console.WriteLine("Done.");
    }
}

When a connection has been created and opened, the code then creates a MySqlCommand object. Note that the SQL query to be executed is passed to the MySqlCommand constructor. The ExecuteReader method is then used to generate a MySqlReader object. The MySqlReader object contains the results generated by the SQL executed on the command object. Once the results have been obtained in a MySqlReader object, the results can be processed. In this case, the information is printed out by a while loop. Finally, the MySqlReader object is disposed of by running its Close method on it.

In the next example, you will see how to use the ExecuteNonQuery method.

The procedure for performing an ExecuteNonQuery method call is simpler, as there is no need to create an object to store results. This is because ExecuteNonQuery is only used for inserting, updating and deleting data. The following example illustrates a simple update to the Country table:

using System;
using System.Data;

using MySql.Data;
using MySql.Data.MySqlClient;

public class Tutorial3
{
    public static void Main()
    {
        string connStr = "server=localhost;user=root;database=world;port=3306;password=******;";
        MySqlConnection conn = new MySqlConnection(connStr);
        try
        {
            Console.WriteLine("Connecting to MySQL...");
            conn.Open();

            string sql = "INSERT INTO Country (Name, HeadOfState, Continent) VALUES ('Disneyland','Mickey Mouse', 'North America')";
            MySqlCommand cmd = new MySqlCommand(sql, conn);
            cmd.ExecuteNonQuery();
        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

        conn.Close();
        Console.WriteLine("Done.");
    }
}

The query is constructed, the command object created and the ExecuteNonQuery method called on the command object. You can access your MySQL database with the mysql command interpreter and verify that the update was carried out correctly.

Finally, you will see how the ExecuteScalar method can be used to return a single value. Again, this is straightforward, as a MySqlDataReader object is not required to store results, a simple variable will do. The following code illustrates how to use ExecuteScalar:

using System;
using System.Data;

using MySql.Data;
using MySql.Data.MySqlClient;

public class Tutorial4
{
    public static void Main()
    {
        string connStr = "server=localhost;user=root;database=world;port=3306;password=******;";
        MySqlConnection conn = new MySqlConnection(connStr);
        try
        {
            Console.WriteLine("Connecting to MySQL...");
            conn.Open();

            string sql = "SELECT COUNT(*) FROM Country";
            MySqlCommand cmd = new MySqlCommand(sql, conn);
            object result = cmd.ExecuteScalar();
            if (result != null)
            {
                int r = Convert.ToInt32(result);
                Console.WriteLine("Number of countries in the World database is: " + r);
            }

        }
        catch (Exception ex)
        {
            Console.WriteLine(ex.ToString());
        }

        conn.Close();
        Console.WriteLine("Done.");
    }
}

This example uses a simple query to count the rows in the Country table. The result is obtained by calling ExecuteScalar on the command object.