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Runtime calculated fields

Posted on 1998-10-28
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Last Modified: 2010-05-18
I'm constructing a table at Runtime and want to use a calculated field to find the product of two other fields in the table.

Anyone tell me how to set up the field etc at runtime. Thanks.
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Question by:cavalry
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2 Comments
 
LVL 8

Accepted Solution

by:
ZifNab earned 20 total points
ID: 1344865
Hi cavalry,

 This should do :

Table1.Active:=false; // Must be false to add Fields to the Dataset
Table1.FieldDefs.Update; // Make sure we have the latest Fields
Monthly:=TFloatField.Create(Table1);
Monthly.FieldName:='Monthly Salary';
Monthly.Calculated:=true;
Monthly.Dataset:=Table1;
Monthly.DisplayFormat:='$#,0.00';
Table1.Active:=true;

Regards, Zif.

ps. don't forget to assign a procedure to OnFieldsCalc event
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LVL 3

Expert Comment

by:rickpet
ID: 1344866
This ones a little more robust...taken from Ray Konopka's book
Custom Delphi 3 Components...highly recommeded...

function CreateCalcField(const FieldName: string; FieldClass: TFieldClass;
                                 Size: Word): TField;
begin
  //Taken from TRzBusinessComponent
  Result := FDataset.FindField(FieldName);
  if Result = nil then begin
    if FieldClass = nil then
      exit;
    Result := FieldClass.Create(Owner);
    try
      Result.FieldName := FieldName;
      if (Result is TStringField) or (Result is TBytesField) or
         (Result is TVarBytesField) then
        Result.Size := Size;
      Result.Calculated := True;
      Result.DataSet := FDataSet;
      Result.Name := GenerateNewFieldName(Owner, FDataset.Name, FieldName);
    except
      Result.Free;
      raise;
    end;
  end;
end;

function GeneratenewFieldName(AOwner: TComponent; const DatasetName: string;
                              const FieldName: string): string;
var
  i: Integer;
  NewName: string;
  Done: Boolean;
function ComponentExists(AOwner: TComponent; const CompName: string): boolean;
var
 i: Integer;
begin
  Result := False;
  for i := 0 to AOwner.ComponentCount -1 do begin
    if AnsiCompareText(CompName, AOwner.Components[i].Name) = 0 then begin
      Result := True;
      Break;
    end;
  end;    // for
end;
begin
  NewName := DatasetName;
  for i := 0 to Length (FieldName) do begin
    if FieldName[i] in ['0'..'9', '_', 'A'..'Z', 'a'..'z'] then
      NewName := NewName + FieldName[i];
  end;
  if ComponentExists(Owner, NewName) then begin
    i := 1;
    Done := False;
    repeat
      inc(i);
      if not ComponentExists(AOwner, Newname+IntToStr(i)) then begin
        Result := NewName + IntToStr(i);
        Done := True;
      end;
    until
      Done;
  end else
    Result := NewName;
end;


Rick
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