Adding a calculated field

[sandy771]

I want to add a calulated field at runtime to a query supplied by a user (I have no idea of what fields/columns are in the query before hand)

My current code is

UniQuery2->Prepare();

field_def = UniQuery2->FieldDefs->AddFieldDef();
field_def->DataType = ftInteger;
field_def->Name = "calc";

for(int f = 0; f < UniQuery2->FieldDefs->Count; f++)
{
field_def = UniQuery2->FieldDefs->Items[f];
CodeSite->Send(" " + field_def->Name);
field = field_def->CreateField(UniQuery2);
if(field->FieldName == "calc")
field->FieldKind = fkCalculated;
}

//CodeSite - lists four fields, including my "calc" field

UniQuery2->Open();

for(int f = 0; f < UniQuery2->FieldDefs->Count; f++)
{
field_def = UniQuery2->FieldDefs->Items[f];
CodeSite->Send(" " + field_def->Name);
}

// codesite shows only three fileds, my calc field is missing!!

what am I doing wrong?

Thanks

[AlexP]

Hello,

There is a code below for adding calculated field in run-time and calculation of this field value.

Code: Select all

type 
  TForm1 = class(TForm)
  ...
    procedure UniQuery1CalcFields(DataSet: TDataSet);
  private
    FCalc: TIntegerField;
  ....
  end;

procedure TForm1.FormCreate(Sender: TObject);
var
  i: integer;
begin
  UniQuery1.FieldDefs.Update;
  for i := 0 to UniQuery1.FieldDefs.Count - 1 do
    UniQuery1.FieldDefs[i].CreateField(UniQuery1);

  FSUM := TIntegerField.Create(UniQuery1);
  FSUM.FieldName := 'Calc';
  FSUM.FieldKind := fkCalculated;
  FSUM.DataSet := UniQuery1;
  UniQuery1.Open;
end;

procedure TForm1.UniQuery1CalcFields(DataSet: TDataSet);
begin
  FCalc.Value := 124;
end;

[sandy771]

Thanks Alex

That doesn't work for me,

I created a test program and connected to a test database (with two fields in my case (name and address)

I then ran the following code

Code: Select all

	TIntegerField *field;

	UniQuery1->SQL->Clear();
	UniQuery1->SQL->Add("select * from test");

	UniQuery1->FieldDefs->Update();

	for(int f = 0; f < UniQuery1->FieldDefs->Count; f++)
	{
		UniQuery1->FieldDefs->Items[f]->CreateField(UniQuery1);
	}

	field = new TIntegerField(UniQuery1);
	field->FieldName = "calc";
	field->FieldKind = fkCalculated;
	field->DataSet = UniQuery1;

	UniQuery1->Open();

	for(int f = 0; f < UniQuery1->FieldDefs->Count; f++)
	{
		Memo2->Lines->Add(UniQuery1->FieldDefs->Items[f]->Name);
	}

The final step of the code only listed the original two fileds, not the new "calc" field.

What am I doing wrong?

Thank You.

[AlexP]

FieldDef are not created for Hidden fields and fields with FieldKind <> fkData .

[sandy771]

OK thanks

[AlexP]

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