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How to determine the current record number of a dataset (Views: 100)


Problem/Question/Abstract:

How to determine the current record number of a dataset

Answer:

If the dataset is based upon a Paradox or dBASE table then the record number can be determined with a couple of calls to the BDE (as shown below). The BDE doesn't support record numbering for datasets based upon SQL tables, so if your server supports record numbering you will need to refer to its documentation.

The following function is given as part of a whole unit and takes as its parameter any component derived from TDataset (i.e. TTable, TQuery, TStoredProc) and returns the current record number (greater than zero) if it is a Paradox or dBASE table. Otherwise, the function returns zero.

For dBASE tables the record number returned is always the physical record number. So, if your dataset is a TQuery or you have a range set on your dataset then the number returned won't necessarily be relative to the dataset being viewed, rather it will be based on the record's physical position in the underlying dBASE table.

uses
  DB, DBTables, DbiProcs, DbiTypes, DbiErrs;

function GetRecordNumber(Dataset: TDataset): Longint;
var
  CursorProps: CurProps;
  RecordProps: RECProps;
begin
  { Return 0 if dataset is not Paradox or dBASE }
  Result := 0;
  with Dataset do
  begin
    { Is the dataset active? }
    if State = dsInactive then
      raise EDatabaseError.Create('Cannot perform this operation ' + 'on a closed dataset');
    { We need to make this call to grab the cursor's iSeqNums }
    Check(DbiGetCursorProps(Handle, CursorProps));
    { Synchronize the BDE cursor with the Dataset's cursor }
    UpdateCursorPos;
    { Fill RecordProps with the current record's properties }
    Check(DbiGetRecord(Handle, dbiNOLOCK, nil, @RecordProps));
    { What kind of dataset are we looking at? }
    case CursorProps.iSeqNums of
      0: Result := RecordProps.iPhyRecNum; { dBASE }
      1: Result := RecordProps.iSeqNum; { Paradox }
    end;
  end;
end;

end.

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