problem with datasource
lazarus / 16-Databases

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notebook · 2011-07-30 19:18

I try example from
http://wiki.lazarus.freepascal.org/Lazarus_Database_Tutorial

but I get errors if I run app from lazarus on button press.

Project project1 raised exception class 'External'. SIGSEGV.
if I run app outside lazarus then I get message Access violation.
problem is in
   ds.DataSet:=query;

if I show data in memo then work

OS is fedora linux 14 32 bit, lazarus 0.9.30, ,31.03.2011

Code: [Select]unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
StdCtrls,
  DBGrids, DbCtrls, Grids, sqldb, postgres, pqconnection,db;

type

  { TForm1 }

  TForm1 = class(TForm)
    Button1: TButton;
    DBGrid1: TDBGrid;
    Memo1: TMemo;

    procedure Button1Click(Sender: TObject);
  private


  public
     conn : TPQConnection;
    query : TSQLQuery;
    transaction : TSQLTransaction;
     ds : TDatasource;
  end;

var
  Form1: TForm1;

implementation

{$R *.lfm}

{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);


begin
  conn := TPQConnection.Create(nil);
  query := TSQLQuery.Create(nil);
  transaction := TSQLTransaction.Create(nil);
  try
    try
      conn.HostName := '127.0.0.1';
      conn.UserName := 'postgres';
      conn.Password := 'postgres';
      conn.DatabaseName := 'postgres';
      conn.Connected := True;
      conn.Transaction := transaction;
      query.DataBase := conn;
      query.SQL.Text := 'select * from my_table';

       query.Open;
       ds.DataSet:=query;
        DBGrid1.DataSource:=ds;


    finally
      query.Free;
      conn.Free;
    end;
  except
    on E: Exception do
      ShowMessage(E.message);
  end;



end;

end.

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Arbee · 2011-08-04 14:26

Although it is not possible to tell for sure without looking at your
form, the place where you have the TDatasource defined suggests that
you have not dropped a TDataSource on the form, but coded it yourself.

If so, then I do not see the TDatasource variable ds being created
anywhere, which would explain the SIGSEGV.

Either code a create of "ds" or drop a TDataSource onto your form (or
better, use a DataModule to separate view and model code).