5.1.5 Working with Stored Procedures

This section illustrates how to work with stored procedures. Putting database-intensive operations into stored procedures lets you define an API for your database application. You can reuse this API across multiple applications and multiple programming languages. This technique avoids duplicating database code, saving time and effort when you make updates due to schema changes, tune the performance of queries, or add new database operations for logging, security, and so on. Before working through this tutorial, familiarize yourself with the CREATE PROCEDURE and CREATE FUNCTION statements that create different kinds of stored routines.

For the purposes of this tutorial, you will create a simple stored procedure to see how it can be called from Connector/Net. In the MySQL Client program, connect to the World database and enter the following stored procedure:

DELIMITER //
CREATE PROCEDURE country_hos
(IN con CHAR(20))
BEGIN
  SELECT Name, HeadOfState FROM Country
  WHERE Continent = con;
END //
DELIMITER ;

Test that the stored procedure works as expected by typing the following into the mysql command interpreter:

CALL country_hos('Europe');

Note that The stored routine takes a single parameter, which is the continent to restrict your search to.

Having confirmed that the stored procedure is present and correct, you can see how to access it from Connector/Net.

Calling a stored procedure from your Connector/Net application is similar to techniques you have seen earlier in this tutorial. A MySqlCommand object is created, but rather than taking an SQL query as a parameter, it takes the name of the stored procedure to call. Set the MySqlCommand object to the type of stored procedure, as shown by the following code snippet:

string rtn = "country_hos";
MySqlCommand cmd = new MySqlCommand(rtn, conn);
cmd.CommandType = CommandType.StoredProcedure;

In this case, the stored procedure requires you to pass a parameter. This can be achieved using the techniques seen in the previous section on parameters, Section 5.1.4, “Working with Parameters”, as shown in the following code snippet:

cmd.Parameters.AddWithValue("@con", "Europe");

The value of the parameter @con could more realistically have come from a user input control, but for simplicity it is set as a static string in this example.

At this point, everything is set up and you can call the routine using techniques also learned in earlier sections. In this case, the ExecuteReader method of the MySqlCommand object is used.

Complete working code for the stored procedure example is shown below:

using System;
using System.Data;

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

public class Tutorial6
{
    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 rtn = "country_hos";
            MySqlCommand cmd = new MySqlCommand(rtn, conn);
            cmd.CommandType = CommandType.StoredProcedure;

            cmd.Parameters.AddWithValue("@con", "Europe");

            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.");
    }
}

In this section, you have seen how to call a stored procedure from Connector/Net. For the moment, this concludes our introductory tutorial on programming with Connector/Net.