CODEWITHSUNDEEP
delphidelphi-xe6tclientdataset
Tarasov
Tarasov

Reputation: 3685

How I can get the changes of a TClientDataset to another TClientDataset?

How can I get from a TClientDataset the changes?

I have a TClientDataset named GetDataset and I have a grid. I want the changes in a new TClientDataset named ChangeDataset.

How can I do this?

Upvotes: 3

Views: 2612

Answers (1)

MartynA
MartynA

Reputation: 30715

If you have a source ClientDataSet CDS1, you should be able to copy the changed records to a second ClientDataSet CDS2 by doing

if CDS1.ChangeCount > 0 then 
  CDS2.Data := CDS1.Delta;

As you'll see if you try that, it gives you a "before" record and one with the change(s). That may not necessarily be what you want - frankly you'd do best to read the Whipple article posted in a comment and in the OLH to get the exact result you might be wanting to achieve. The point is, all the information you need is in the source CDS until you flush it away (by calling ApplyUpdates() - after that, if it succeeds, the change log is empty).

If you look at the rows in CDS2, it's not immediately obvious how you tell whether a particular field contains a changed value and how you distinguish one that does from one which is just empty. Istr there was a very good post quite a long time ago in one of the Borland NTTP newsgroups by their Mark Edington, I think, explaining how to do this. Basically, it's a question of evaluating VarIsClear on the field's NewValue property:

if VarIsClear(CDS2.Fields[i].NewValue) then 
// means Fields[i] does not have a changed value

Incidentally, since you can save the state of a CDS to XML, you can use XML manipulations, e.g. with a DOM parser such is the Windows built-in one (see MSXML.Pas) to do easily many things which are troublesome to do using the TDataSet paradigm.

Upvotes: 11

Related Questions