How to force a Client DataSet to recalculate calculated and internal calculated fields?

Question

I have a ClientDatSet with a few fkInternalCalc fields. The CDS is not linked to any provider; instead it's filled on the fly. How can I force CDS to recalculate all the "calculable" fields? I can not call Refresh() because there is no provider to refresh data from. The only way I have come with so far has been to navigate through all records, which is not the best way.

PS: I have read this question and this post, but I'm hoping for a more elegant way.

@SertacAkyuz I haven't tried it yet. Doesn't closing a client dataset clear all the data in it? — iMan Biglari, Jul 28 '13 at 12:24
@SertacAkyuz I was afraid so... What does `Resync()` do? Any ideas? — iMan Biglari, Jul 28 '13 at 12:33
@Iman: Would you please explain why you need to force the fields calculation? It happens automaticaly everytime a field changes in response to an internal dataset event named **deFieldChanged**. There is a protected method named **TDataset.CalculateFields** that fires the process to the current record, but it is not intented to be used by any code other than the TDataset's (or a subclass of it). All this because, theoretically, a programmer wouldn't need to fire the calculation process him/herself. — AlexSC, Jul 28 '13 at 13:53
@iMan - It fetches data from the database if I'm not mistaken. The only method I was able to figure out which does not fetch data, is the one I had mentioned in a comment to the answer of the question that you linked. You've most probably already seen it. — Sertac Akyuz, Jul 28 '13 at 14:11
@Uwe: the code for calculating InternalCalc fields (**RefreshInternalCalcField**) is called by the same method that calls **CalculateFields**. It's an inner procedure declared in the scope of **DataEvent**. This is all true in Deelhi XE3, at least. So, for that particular version of Dephi, I believe it applies for both Calculated fields and InternalCalc fields. — AlexSC, Jul 28 '13 at 14:27
@AlexSC I need to force fields calculation because the calculated fields need to reflect changes in external events. — iMan Biglari, Jul 28 '13 at 18:05

Uwe Raabe · Accepted Answer · 2013-07-28T13:55:25.143

8

I achieve that with a helper (stripped here to the necessary), which allows to call the protected methods without any hack. Make sure to check for DataSet.State = dsInternalCalc inside OnCalcFields for fkInternalCalc fields.

type
  TClientDataSetHelper = class helper for TClientDataSet
  public
    function AssureEditing: Boolean;
    procedure InternalCalc;
  end;

function TClientDataSetHelper.AssureEditing: Boolean;
begin
  result := not (State in [dsEdit, dsInsert]);
  if result then
    Edit;
end;

procedure TClientDataSetHelper.InternalCalc;
var
  needsPost: Boolean;
  saveState: TDataSetState;
begin
  needsPost := AssureEditing;
  saveState := setTempState(dsInternalCalc);
  try
    RefreshInternalCalcFields(ActiveBuffer);
  finally
    RestoreState(saveState);
  end;
  if needsPost then
    Post;
end;

This can easily be expanded for normal calculated fields using CalculateFields. Although this shouldn't be necessary as calculated fields are recalculated whenever any other data field changes.

edited Jul 28 '13 at 13:55

answered Jul 28 '13 at 13:18

Uwe Raabe

45,288
3
82
130

I tried this and get *"[dcc32 Error] dMyDataModule.pas(151): E2389 Protected member 'TDataSet.RefreshInternalCalcFields' is inaccessible here"*. – GolezTrol Jun 16 '15 at 08:16
@GolezTrol, looks like a bug. Works in XE3, but not in XE7 and XE8 (currently cannot check for XE4 to XE6). Other protected members are perfectly accessible: "setTempState", "RestoreState". Just reported as RSP-11337. – Uwe Raabe Jun 16 '15 at 10:23
To narrow it down, I was on XE5. Thanks for testing! I've solved it now using the more classic class helper: typecasting to a locally defined `THackClientDataSet = class(TClientDataSet)`. – GolezTrol Jun 16 '15 at 10:53

score -1 · Answer 2 · edited Sep 17 '17 at 11:54

-1

This is a bit of a hack, but it works!

DBGrid.Height := 30; 
DBGrid.Height := 200; // Refresh all Rows after first
CalculatedProc(DataSet); // Refresh first calculated fields. (Write name of your calculate procedure)

edited Sep 17 '17 at 11:54

Gilles Gouaillardet

8,193
11
24
30

answered Sep 17 '17 at 11:03

Ivan Ko

9
2

1. Used the Delphi default function 2. Shot 3. Simple – Ivan Ko Sep 17 '17 at 12:05
4. Faster then use change states! – Ivan Ko Sep 17 '17 at 12:19
1

would you mind editing the answer and elaborating a bit here ? – Gilles Gouaillardet Sep 17 '17 at 12:20
Why don't you call "refresh" if you want to refresh all rows? – Sertac Akyuz Sep 17 '17 at 14:35
Refresh reload data from server. – Ivan Ko Sep 17 '17 at 16:25
Gilles, sorry. Can you tell me what you want some more? You want for I renamed "CalculatedProc" to "InternalCalc"? I think this is wery simple code for everyone. One can adapted to same tasks. – Ivan Ko Sep 17 '17 at 16:41
Where do you think the record buffer is retrieved from when you increase grid's height? – Sertac Akyuz Sep 17 '17 at 19:30
When the window of grid is redrawn, the calculated fields are recalculated. But it is worked, when data of buffer show in the grid. – Ivan Ko Sep 19 '17 at 05:12
No, data of buffer is not kept magically at some place when you contract the number of rows shown in the grid. When you later increase visible number of rows, data is retrieved from server to fill the necessary record buffer. – Sertac Akyuz Sep 19 '17 at 21:30

How to force a Client DataSet to recalculate calculated and internal calculated fields?

2 Answers2