[Mono-list] Npgsql error

[Emil Emilov]

Also another tip: you don't need to explicitly set connection etc. to null.
Cosider following improvement:

IDbConnection dbcon;
IDbCommand dbcmd;
IDataReader reader;
try {
  dbcon = new NpgsqlConnection(connectionString);
  dbcon.Open();
  dbcmd = dbcon.CreateCommand();
  string sql =
    "SELECT operatingsystem, nodeid " +
    "FROM assets";
  dbcmd.CommandText = sql;
  reader = dbcmd.ExecuteReader();
  while(reader.Read()) {
     string operatingsystem = (string) reader["operatingsystem"];
     string nodeid = (string) reader["nodeid"];
     Console.WriteLine("OS: " +
   operatingsystem + " " + nodeid);
  }
} catch (Exception ex)  {
  // do stuff, rollback transaction
} finally {
  // cleanup, even if error occurs, closing the reader is important because while it is open no other reader can be opened
  if (reader!=null) reader.Close();
  if (dbcmd!=null) dbcmd.Close();
  if (dbcon!=null) dbcon.Close();
}

Fabian Salamanca Dominguez wrote:
> 
> Hi
> 
> I tried to compile a simple C# program and access a Postgresql DB but I 
> got this error in runtime (it compiled with no errors) :
> 
> [fsalaman at ipdserver Mono]$ mcs dbaccess.cs  -r:Npgsql.dll -r:System.Data.dll
> [fsalaman at ipdserver Mono]$ mono dbaccess.exe
> 
> Unhandled Exception: System.InvalidCastException: Cannot cast from 
> source type to destination type.
> in <0x000e1> dbAccess:Main (System.String[] args)
> 
> ****************
> 
> This is the code:
> 
> using System;
> using System.Data;
> using Npgsql;
> public class dbAccess
>  {
>     public static void Main(string[] args)
>     {
>        string connectionString =
>           "Server=localhost;" +
>           "Database=opennms;" +
>           "User ID=opennms;" +
>           "Password=opennms;";
>        IDbConnection dbcon;
>        dbcon = new NpgsqlConnection(connectionString);
>        dbcon.Open();
>        IDbCommand dbcmd = dbcon.CreateCommand();
>        string sql =
>            "SELECT operatingsystem, nodeid " +
>            "FROM assets";
>        dbcmd.CommandText = sql;
>        IDataReader reader = dbcmd.ExecuteReader();
>        while(reader.Read()) {
>             string operatingsystem = (string) reader["operatingsystem"];
>             string nodeid = (string) reader["nodeid"];
>             Console.WriteLine("OS: " +
>                  operatingsystem + " " + nodeid);
>        }
>        // clean up
>        reader.Close();
>        reader = null;
>        dbcmd.Dispose();
>        dbcmd = null;
>        dbcon.Close();
>        dbcon = null;
>     }
>  }
> 
> What am I doing wrong?
> 
> Thanks!!!
> -- 
> Fabian
> 
> 
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-- 
Emil R. Emilov
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