CODEWITHSUNDEEP
delphiaggregatetclientdataset
ivarec
ivarec

Reputation: 2612

How do I use an aggregate field in a TClientDataSet that is a BIGINT (TLargeintField)?

I need to calculate the Max value of a field, but I'm having troubles doing so. Let's say that my field is named 'VALUE0'. I would like to use the aggregate functions of TClientDataSet to do so. What should I do?

This code will fail only with fields that are BIGINT in my SQL table:

function TFrmIo.GetMaxY(): Integer;
var
  Max0: Integer;
  FieldMax0: TAggregateField;
begin
  if cds.Active then cds.Close;

  FieldMax0 := TAggregateField.Create(cds);
  FieldMax0.FieldName := 'MAX0';
  FieldMax0.Calculated := true;
  FieldMax0.ResultType := ftLargeint;
  FieldMax0.FieldKind := fkAggregate;
  FieldMax0.DataSet := cds;
  FieldMax0.Expression := 'MAX(VALUE0)';
  FieldMax0.Active := true;

  cds.Open;

  Max0 := Integer(FieldMax0.Value);
end;

I get this exception on the "cds.Open" line:

Exception class EDBClient with message 'Type mismatch in expression.'

EDIT

As requested in the comment, the class name of VALUE0's field is TLargeintField and the FieldKind is fkData.

EDIT 2

Changed the question and some parts in the text because now I know that the problem is about BIGINT vs INTEGER in TClientDataSet aggregate functions.

Upvotes: 3

Views: 5764

Answers (2)

Yevhen Putsil
Yevhen Putsil

Reputation: 11

As a workaround one could use 'MAX(VALUE0 * 1)' or 'MAX(VALUE0 + 0)' for Expression. Then your ResultType will be ftFloat. Just don't forget to round the value when you access it: Max0 := Round(FieldMax0.Value); (floats tend to have a tiny tail sometimes :)

Upvotes: 1

ivarec
ivarec

Reputation: 2612

As pointed out by Sertac Akyuz, it is not possible to do so on Delphi 2010 and below. Seems to be fixed in Delphi XE, although I haven't tested it.

http://qc.embarcadero.com/wc/qcmain.aspx?d=83610

Upvotes: 1

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