Failing to update a table - delphi

Question

I have a boolean field in cxGrid (represented as a checkbox inside the grid).
I am trying to do an update of the very same record when user sets the checkbox as checked.
I tried this:
procedure TDataModule3.ABSTable2BeforePost(DataSet: TDataSet);
begin
if DataModule3.ABSTable2.FieldByName('DONE').AsBoolean = True then
with Datamodule3.ABSQuery4 do begin
Datamodule3.ABSQuery4.Close;
Datamodule3.ABSQuery4.SQL.Clear;
Datamodule3.ABSQuery4.SQL.Text :='UPDATE MYTABLE SET USER=:a1 where TW_ID =:a2';
Datamodule3.ABSQuery4.Params.ParamByName('a1').AsString := MainForm.AdvOfficeStatusBar1.Panels[3].Text ;
Datamodule3.ABSQuery4.Params.ParamByName('a2').AsInteger := Datamodule3.ABSTable2.FieldByName('TW_ID').AsInteger;
Datamodule3.ABSQuery4.ExecSQL;
end;
end;
I get :
First chance exception at $00B6E33F. Exception class $C0000005 with message 'access violation at 0x00b6e33f: read of address 0x000003a0'. Process Project1.exe (4916)
What am I doing wrong ?
Edit: I tried the suggestion.
/
if ABSTable2.FieldByName('Done').AsBoolean = True then
begin
ABSQuery4.Close;
ABSQuery4.SQL.Clear;
ABSQuery4.SQL.Text :='UPDATE mytable SET user=:a1 where TW_ID=:a2 ';
ABSQuery4.Params.ParamByName('a1').AsString := ABSQuery1.FieldByName('USER').asString ;
ABSQuery4.Params.ParamByName('a2').AsInteger := ABSTable2.FieldByName('TW_ID').AsInteger;
ABSQuery4.ExecSQL;
end;
I have removed the reference to the main form and added the query syntax as the AdvOfficeStatusBar1.Panels[3].Text gets its data from it.
Now I get: Absolute Engine error : The table is locked.

Answer 1

Remove the DataModule3 from the beginning of all of the lines of code.
You're using an instance variable inside the methods of a class. If the instance is named anything other than DataModule3 or DataModule3 hasn't been created, your code will fail.
The proper way to write the code would be (see the NOTE below):
procedure TDataModule3.ABSTable2BeforePost(DataSet: TDataSet);
begin
if Self.ABSTable2.FieldByName('DONE').AsBoolean = True then
begin
Self.ABSQuery4.Close;
Self.ABSQuery4.SQL.Clear;
Self.ABSQuery4.SQL.Text :='UPDATE MYTABLE SET USER=:a1 where TW_ID =:a2';
// See NOTE below
Self.ABSQuery4.Params.ParamByName('a1').AsString := MainForm.AdvOfficeStatusBar1.Panels[3].Text ;
Self.ABSQuery4.Params.ParamByName('a2').AsInteger := Self.ABSTable2.FieldByName('TW_ID').AsInteger;
ABSQuery4.ExecSQL;
end;
end;
NOTES
The Self is optional. You could write each without the Self. and it would work equally as well in this case. Self refers to the current instance of the object, rather than a specific named instance like DataModule3 does.
You should find a way to remove the reference to MainForm and a visual component by adding an instance variable or property to the datamodule class instead that you can refer to in your code. Hard-coding in the MainForm can cause the same kind of problems that hard-coding in DataModule3 - it's a specific instance name rather than just being the current instance of something. If you rename your MainForm to something else, your code won't compile. If you replace MainForm with a different form, but there's another MainForm in scope that hasn't been created yet, your code will also crash.