[SOLVED] DataModule messed me up
lazarus / 16-Databases

----------------------------------------------------------------------
guest48180 · 2019-07-25 12:35

On a form, I had a TSQLite3Connection, TSQLTransaction,
TSQLTransaction, and a TSQLQuery. Life was good. I got it wired up and
it was rolling. But then I decided to show off a little. So I added
the TSQLite3Connection and the TSQLTransaction to a TDataModule, named
DM1. On Unit1, I added
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i uses 
Unit2;Made all the necessary changes to the prior uses of
TSQLite3Connection and TSQLite3Connection on Unit1, i.e.:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i
DM1.SQLite3Connection1.Connected := True;  DM1.SQLTransaction1.Active
:= True;But now, when I run it, I get an error:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i Project
ProjectName raised exception class 'External SIGSEGV'and references
this line, which is also the first line in Unit1 that makes reference
to my DM1 of Unit2:
Code: [Select]DM1.SQLite3Connection1.DatabaseName := 'data.db';
Again, all of this worked until I started using the DataModule. I
don't mind putting it all back on one form, but the DataModule seems
kind of handy.

Here's all the code on Unit1:
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i unit
Unit1; {$mode objfpc}{$H+} interface uses  Classes, SysUtils, db,
sqldb, sqlite3conn, Forms, Controls, Graphics, Dialogs,  DBGrids,
DBCtrls; type   { TForm1 }   TForm1 = class(TForm)    DataSource1:
TDataSource;    DBGrid1: TDBGrid;    DBNavigator1: TDBNavigator;   
SQLQuery1 : TSQLQuery ;    procedure DBNavigator1Click(Sender:
TObject; Button: TDBNavButtonType);    procedure FormCreate(Sender:
TObject);  private   public   end; var  Form1:
TForm1; implementation {$R *.lfm}uses  Unit2; { TForm1 } procedure
TForm1.DBNavigator1Click(Sender: TObject; Button:
TDBNavButtonType);begin  case Button of  nbPost:    begin     
SQLQuery1.ApplyUpdates;      DM1.SQLTransaction1.CommitRetaining;   
end;  nbDelete:    begin      SQLQuery1.ApplyUpdates;     
DM1.SQLTransaction1.CommitRetaining;    end;   end;end;   procedure
TForm1.FormCreate(Sender: TObject);begin 
DM1.SQLite3Connection1.DatabaseName := 'data.db';  SQLQuery1.SQL.Text
:= 'PRAGMA foreign_keys = ON';  SQLQuery1.ExecSQL; 
DM1.SQLTransaction1.Commit;   SQLQuery1.SQL.Text :=    'CREATE TABLE
IF NOT EXISTS customers(' +    'cust_id INTEGER PRIMARY KEY
AUTOINCREMENT, ' +    'cust_name VARCHAR(30) NOT NULL)'; 
DM1.SQLite3Connection1.Connected := True;  DM1.SQLTransaction1.Active
:= True;  SQLQuery1.ExecSQL;  DM1.SQLTransaction1.Commit;  
SQLQuery1.SQL.Text :=    'CREATE TABLE IF NOT EXISTS sites(' +   
'site_id INTEGER PRIMARY KEY AUTOINCREMENT, ' +    'site_name
VARCHAR(30) NOT NULL, ' +    'site_cust VARCHAR(30) NOT NULL, ' +   
'FOREIGN KEY (site_cust) REFERENCES customers(cust_id) '  +    'ON
UPDATE CASCADE ON DELETE CASCADE)';  SQLQuery1.ExecSQL; 
DM1.SQLTransaction1.Commit;   SQLQuery1.SQL.Text := 'select * from
customers';  SQLQuery1.Open;   DBGrid1.Columns[0].Visible :=
False;end; end. 
What am I doing wrong?

----------------------------------------------------------------------
JanRoza · 2019-07-25 12:55

You're using DM1 regularly but is nowhere declared.
Whant's the name of your DataModule unit?
Add that name to your uses clause (so where you now have uses unit2,
change it to uses unit2, <datamodule unit name>.

----------------------------------------------------------------------
lucamar · 2019-07-25 13:38

Quote from: JanRoza on July 25, 2019, 02:55:08 pmYou're using DM1
regularly but is nowhere declared.
Whant's the name of your DataModule unit?
From the original post, one may assume that unit2 is the DataModule
unit and that DM1 is declared inside? If not it wouldn't compile,
would it? There would be lots of "Identifier not found" compile-time
errors.

The most probable cause of the error is that the form's OnCreate event
is being triggered before the data module is (fully) created, so it
references objects that don't exist yet. Check the creation order
either in the "Project options" windows or directly in the program
source (menu "Project->View project source").

Don't forget to check that the data module is on the auto-create list!
If not, its objects will never be "alive"

----------------------------------------------------------------------
guest48180 · 2019-07-25 14:24

lucamar:

That was it. I moved the code to OnActivate for Form 1, and it runs
good now. Thanks for pointing that out to me. That got me rolling
again

----------------------------------------------------------------------
lucamar · 2019-07-25 14:52

Glad it helped. I've fallen on that trap quite a few times too