Reversing the Master-Detail connection in Delphi

Question

I have 2 tables which are connected using master-detail connection. I need the connection reversed on creation of Form2 - so the master table becomes the detail table, and the detail table becomes the master table.

I tried doing this, and the program compiles, but doesn't work the way I want it to (the previous connection breaks, but it's not reversed, so the program kinda works like the tables aren't connected at all):

    Form1.ADOTableDetail.MasterSource.Destroy;
    Form1.ADOTableMaster.MasterSource :=  Form1.DataSourceDetail;
    Form1.ADOTableMaster.MasterFields := 'the_field_that_connects_them';

Any ideas on how I might achieve this?

score 6 · Accepted Answer · answered May 22 '11 at 14:29

6

Don't destroy the MasterSource!

In order to break the relationship do

Form1.ADOTableDetail.MasterSource:= nil;
Form1.ADOTableDetail.MasterFields:= '';

than use this to reroute the MasterDetail

Form1.ADOTableMaster.MasterSource :=  Form1.DataSourceDetail;
Form1.ADOTableMaster.MasterFields := 'the_field_that_connects_them';

Also never call .Destroy directly, use .Free instead.
Free does an extra check to see if the reference you are Freeing is not nil, preventing some Access Violations.

answered May 22 '11 at 14:29

Johan

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@Radiant, thanks for re-accepting my answer, you seem torn between the two :-). *Damn now I've got that annoying song in my head*. – Johan May 23 '11 at 22:09
Hehe. No problem. Yes, I really was torn between which one I should accept - it's the hard part of being a StackOverflow user :D Anyways, I accepted your answer again, because NGLN's code gave me false sense of security. It could swap the relations only once, which I didn't notice. In the end I endedup writing my own sucky version of the code. I thank you both again, though! :D – Radiant May 23 '11 at 22:22

score 3 · Answer 2 · answered May 22 '11 at 14:36

3

procedure TForm1.ExchangeMasterDetail;
begin
  ADOTableDetail.Close;
  ADOTableMaster.Close;
  ADOTableMaster.MasterFields := ADOTableDetail.IndexFieldNames;
  ADOTableMaster.IndexFieldNames := ADOTableDetail.MasterFields;
  ADOTableDetail.IndexFieldNames := '';
  ADOTableDetail.MasterFields := '';
  ADOTableDetail.MasterSource := nil;
  ADOTableMaster.MasterSource := DataSourceDetail;
  ADOTableDetail.Open;
  ADOTableMaster.Open;
end;

answered May 22 '11 at 14:36

NGLN

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Wow I tried this one now, and it's actually more flexible! Thanks! – Radiant May 22 '11 at 15:25

score 0 · Answer 3 · edited Oct 25 '13 at 22:22

0

Just set the Master table Active propriety to false.

Then do what you wanna todo and set it back to true.

edited Oct 25 '13 at 22:22

Diosney

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answered Oct 25 '13 at 22:00

Samir

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Reversing the Master-Detail connection in Delphi

3 Answers3