RAD Studio My sample to how use IFDStanExpressionEvaluator to create a expression and evaluate it using a Interbase table values

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My sample to how use IFDStanExpressionEvaluator to create a expression and evaluate it using a Interbase table values
by Emailx45

Спойлер: Content

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• the Interface is used for Evaluator of expressions, like in LiveBinding "magic"
• as Interface, it dont need be "released", but is necessary "Null it" before close your table!
• as necessary activate your table before create the expression to evaluate
• as necessary re-positionate the cursor for next records, before use it!
• is necessary study its use in each case!

/* Table: MYORACLETB, Owner: SYSDBA */
CREATE TABLE MYORACLETB 
(
        ID    INTEGER NOT NULL,
        MYNUMERIC2X0    NUMERIC(2, 0),
        MYNUMERIC4X0    NUMERIC(4, 0),
        MYNUMERIC8X0    NUMERIC(8, 0),
        MYNUMERIC18X0    NUMERIC(18, 0),
        MYNUMERIC20X4    NUMERIC(18, 4)
);

/* Meta data descriptions.  This syntax requires InterBase 2020 or higher.  Some tables require ODS18 and higher */

Спойлер: Source code using Interbase table for test

procedure TForm1.btnUsingIFDStanExpressionEvaluatorClick(Sender: TObject);
var
  lIFDSExpEval: IFDStanExpressionEvaluator;
  lResulted   : Variant;
  lExpression : string;
begin
  lExpression := '((MYNUMERIC2X0 + MYNUMERIC4X0) + MYNUMERIC8X0)'; // cannot contain aggregate funcions!!!
  //
  try
    FDQuery1.Open(); // before, it's necessary open your dataset!
    //
    if FDQuery1.IsEmpty then // are you want a exception?
    begin
      ShowMessage('Hey man, where are the values to evaluate?' + sLineBreak + 'So, I''m going to fuck you baby!');
      exit;
    end;
    //
    // dataset should be active!
    lIFDSExpEval := FDQuery1.CreateExpression(lExpression);
    //
    // This method returns the evaluator, which can be used several times to effectively
    // evaluate a specified expression by calling its Evaluate method. The evaluator is
    // associated with the current record. After the position is changed, the application
    // must adjust the evaluator
    lResulted := lIFDSExpEval.Evaluate;
    //
    ShowMessage(lResulted);
    //
    FDQuery1.Next; // next record... same evaluator expression.
    //
    if not FDQuery1.Eof then // testing EOF for "end" evaluator-life!
    begin
      lIFDSExpEval.DataSource.Position := FDQuery1.GetRow;
      //
      lResulted := lIFDSExpEval.Evaluate;
      //
      ShowMessage(lResulted);

    end;
    //
    // IMPORTANT: is necessary before close your dataset! dont need release it, is a Interface!
    lIFDSExpEval := nil;
    //
    FDQuery1.Close;
  except
    on E: Exception do
      ShowMessage('My Error: ' + sLineBreak + E.Message);
  end;
end;

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