NullReferenceException in MySqlClient.NativeDriver

Question

I have a long running program that exectues some mySQL-Queries every 5 minutes (timed thread). After it has run for approximately 10 hours a NullReferenceException is thrown with the following stacktrace:

at MySql.Data.MySqlClient.NativeDriver.GetResult(Int32& affectedRow, Int32& insertedId)
   bei MySql.Data.MySqlClient.Driver.GetResult(Int32 statementId, Int32& affectedRows, Int32& insertedId)
   at MySql.Data.MySqlClient.Driver.NextResult(Int32 statementId)
   at MySql.Data.MySqlClient.MySqlDataReader.NextResult()
   at MySql.Data.MySqlClient.MySqlDataReader.Close()
   at MySql.Data.MySqlClient.MySqlCommand.ResetReader()
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteReader(CommandBehavior behavior)
   at MySql.Data.MySqlClient.MySqlCommand.ExecuteNonQuery()
   at MyOwnProgram.Mysql.sendData(String sqlCommmand)

The sendData method is the following (lockDB is of type Object)

public void sendData(string sqlCommmand) {
            try {
                using(MySqlCommand command = connection.CreateCommand()) {
                    command.CommandTimeout = 5;
                    command.CommandText = sqlCommmand;
                    lock(lockDB) {
                        command.ExecuteNonQuery();
                    }
                }
            } catch(MySqlException e) {
                throw e;
            } catch(Exception e) {
                // do some logging
            }
        }

The connection is opened when calling the constructor of the mySQL-Class and disposed when calling the destructor or calling dispose(). Can someone tell me what I did wrong?

Answer 1

I would recommend you leaving the connection handling to ADO.NET:

public void sendData(string sqlCommmand) 
{
    using (var con = new MySqlConnection(ConnectionString))
    using(var cmd = con.CreateCommand()) 
    {
        con.Open();
        cmd.CommandTimeout = 5;
        cmd.CommandText = sqlCommmand;
        cmd.ExecuteNonQuery();
    }
}

You no longer need the finally statement. You could add try/catch if you need to log something but make sure to propagate the exception and not consume it.