I am using this code but getting "Object reference not set to an instance of an object.".

This is the code and below it is the error message:

private void generate_report()

npg_connection = new NpgsqlConnection("Server=www.db.2connectbahrain.com;Port=5432;User Id=jassim_rahma;Password=731004167;Database=billing;");

// npg_command.CommandText = "Select category_title FROM reports_category ORDER BY category_title";

npg_command.CommandText = "select * from cdr where local_gateway_start_dt between '2006-08-01 00:00:00' and '2006-08-01 23:59:59' and originator_ip = '80.88.247.115' and dest_reg_id = '2connect_pbx' and called_num_e164 in('16500110', '16500199') and error_description != ''";

MessageBox.Show(npg_command.CommandText);

while (npg_reader.Read())

MessageBox.Show(npg_reader.GetValue(0).ToString());

and here s the error message:

System.NullReferenceException was unhandled
Message="Object reference not set to an instance of an object."
Source="CDR Report"
StackTrace:
at CDR_Report.main_form.generate_report() in C:\Documents and Settings\jassim\My Documents\Visual Studio 2005\Projects\CDR Report\CDR Report\main_form.cs:line 31
at CDR_Report.main_form.btnGenerate_Click(Object sender, EventArgs e) in C:\Documents and Settings\jassim\My Documents\Visual Studio 2005\Projects\CDR Report\CDR Report\main_form.cs:line 58
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.DebuggableCallback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
at System.Windows.Forms.UnsafeNativeMethods.DispatchMessageW(MSG& msg)
at System.Windows.Forms.Application.ComponentManager.System.Windows.Forms.UnsafeNativeMethods.IMsoComponentManager.FPushMessageLoop(Int32 dwComponentID, Int32 reason, Int32 pvLoopData)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoopInner(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.ThreadContext.RunMessageLoop(Int32 reason, ApplicationContext context)
at System.Windows.Forms.Application.Run(Form mainForm)
at CDR_Report.Program.Main() in C:\Documents and Settings\jassim\My Documents\Visual Studio 2005\Projects\CDR Report\CDR Report\Program.cs:line 17
at System.AppDomain.nExecuteAssembly(Assembly assembly, String[] args)
at System.AppDomain.ExecuteAssembly(String assemblyFile, Evidence assemblySecurity, String[] args)
at Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

Which line throws the exception? My guess is that npg_command isn't initialized properly. Where is this variable declared (and initialized)?

Btw: you might want to edit your original post and delete connection string information from it as you're currently exposing a very sensitive information to the rest of the world...

Andrej

Andrej Tozon wrote:

Btw: you might want to edit your original post and delete connection string information from it as you're currently exposing a very sensitive information to the rest of the world...

I second that....!!

Yeah, you need to create an instance of the command...

npg_command = new NpgsqlCommand(yourCommandText, CommandType.Text, NpgsqlConnection);

In at least one of your data rows column(0) is null.

As a result, object reference, GetValue(0), is not set to an instance of an object.

And so, GetValue(0).ToString() becomes (null).ToString()

where .ToString() does not have an object reference.

Additionally, you only need to open the connection once.

Good luck.

Fasty1 wrote:

And so, GetValue(0).ToString() becomes (null).ToString()

Actually, I believe that in this case, GetValue() would return a DBNull, not null. And DBNull.Value *is* a value, so the statement in question would execute without throwing an exception...

Andrej

Try this:

if (!npg_reader.IsDBNull(0)) MessageBox.Show(npg_reader.GetValue(0).ToString());

And I agree, initiate command properly if you did not and open connection if it is not opened before.