Cannot execute mysql store procedure with out parameter in asp.net - asp.net

Question

I have this store procedure with out parameter
DELIMITER $$
CREATE DEFINER=`root`#`localhost` PROCEDURE `usp_count_rows`(OUT total int)
BEGIN
SELECT COUNT(*)
FROM address_book.persons;
END
I want to use it in asp.net page. I write this code behind:
string commandText = "usp_count_rows";
MySqlConnection conn = new MySqlConnection(ConfigurationManager.ConnectionStrings["mySqlString"].ConnectionString);
MySqlCommand cmd = null;
try
{
cmd = new MySqlCommand(commandText, conn);
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.Add("total", MySqlDbType.Int32);
cmd.Parameters["total"].Direction = ParameterDirection.Output;
conn.Open();
cmd.ExecuteNonQuery();
int total = (int)cmd.Parameters["?total"].Value;
}
catch (MySqlException ex)
{
MessageBox.Show(ex.Message);
}
finally
{
conn.Clone();
}
and i got this error message
Specified cast is not valid.
fot the line
int total = (int)cmd.Parameters["?total"].Value;
What should I do to make the code work. And another thing I want ot use the result in aspx page. Something like this: Total number of rows: (result from store procedure). Do you have some suggestions?

Answer 1

This is happening because your SP doesn't return any parameters, just result of the query. And for a stored procedure like this you do not need any parameters - even output ones, so redefine your SP simple as
CREATE DEFINER=`root`#`localhost` PROCEDURE `usp_count_rows`
BEGIN
SELECT COUNT(*)
FROM address_book.persons;
END
Then in you C# get rid of lines (remove them completely):
cmd.Parameters.Add("total", MySqlDbType.Int32);
cmd.Parameters["total"].Direction = ParameterDirection.Output;
and replace these lines:
cmd.ExecuteNonQuery();
int total = (int)cmd.Parameters["?total"].Value;
with this one line:
int total = Convert.ToInt32(cmd.ExecuteScalar());
ExecuteScalar method executes your SP/Query and returns first column of first row of that query (in your case it will be the only column and the only row with the Count(*)).
Oh by the way in your Finally block it should be conn.Close() not conn.Clone(), but I think it's simple a type.
As for displaying results on the ASPX page - there're multiple ways depending on where and how you want to display it. For example you can add a Label control to your page and execute something like:
Label1.Text = "Total number of rows: " + total.ToString();