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Caruso
Asked: 2020-06-28 07:35:10 +0800 CST 2020-06-28 07:35:10 +0800 CST

How to update TClientDataSet when changing DBEdit

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I have a price field in a TClientDataSet that comes from the database but it is calculated, that is, it is saved, but it respects a formula according to freight cost and taxes.

The formula works well mathematically and I have it in the afterpost event:

procedure TDataModule1.cdsproductosAfterPost(DataSet: TDataSet);
begin
 with DataModule1 do
 begin
DataModule1.cdsproductos.Open;

DataModule1.cdsproductos.Edit;
cdsproductosprecioactual.AsFloat:=cdsproductosCosto.AsFloat* 
(cdsproductosGanancia.AsFloat/100)+       
cdsproductosCosto.AsFloat+cdsproductosRedondeo.AsFloat + (cdsproductosCosto.AsFloat * 
(cdsproductosImpuesto.AsFloat/100))+cdsproductosFlete.AsFloat;


end;
end;

So my question is: how do I update the price DBEdit when changing any DBEDit that influences the formula, example: when changing the cost, the price must change and be saved without having to click on the save button.

delphi

1 Answers

  1. Best Answer

    You can use the event OnChangeof the fields that are part of the formula, in this way Precioit will be updated automatically every time the value of any of these fields changes, without waiting until after posting in the record.

    To achieve this, you can start by factoring the formula code into a separate method, say:

    type
  TDataModule1 = class(TDataModule)
  // declaraciones...
  private
    procedure CalcularPrecio;
    // y más declaraciones...
  end;


  procedure TDataModule1.CalcularPrecio;
  begin
    cdsproductosprecioactual.AsFloat := 
        cdsproductosCosto.AsFloat * (cdsproductosGanancia.AsFloat/100)
      + cdsproductosCosto.AsFloat
      + cdsproductosRedondeo.AsFloat 
      + cdsproductosCosto.AsFloat * (cdsproductosImpuesto.AsFloat/100)
      + cdsproductosFlete.AsFloat;
  end;

    CostoSo let's say this calculation should be fired whenever any of the , Redondeo, Ganancia, fields change Impuesto(I don't know if I missed any, but you get the picture), you can write event handlers for OnChangeeach of these fields and call the method CalcularPrecio, which would look something like:

    procedure TDataModule1.cdsproductosCostoChange(Sender: TField);
begin
  CalcularPrecio;
end;

procedure TDataModule1.cdsproductosRedondeoChange(Sender: TField);
begin
  CalcularPrecio;
end;

//etc...

    Good practices

    I have noticed that you use a statement within your code, like this:

    procedure TDataModule1.cdsproductosAfterPost(DataSet: TDataSet);
begin
  with DataModule1 do
  begin
    ....
  end
end;

    I don't know exactly what you want to achieve, but in my opinion, this statement is not only not necessary, but it is superfluous and could cause problems if you create more than one instance of the class at run time in the future. . When any method of the class is cast, TDataModule1you already have access to all members of the class for the instance on which the method was cast. These members do not need to be referenced with a variable.

    I've also seen a couple of other details:

    • You use the method AfterPostto modify data from the same record that you just inserted/updated in the underlying table in the database (I understand that is not what you want in the case of Precio, but if you still use it in other cases, I recommend doing it in el BeforePost, which is fired just before sending the insert/modify to the engine.

      This will prevent any record from being outdated in the dataset if something fails during the execution of the AfterPost.

    • BeforePostThe / methods AfterPostand, in general, most of the DataSet are called while the dataset is open, you do not need to open it , which you do in the first line of code:

      DataModule1.cdsproductos.Open;

      That line is unnecessary, since this event will never be launched on a closed data set.

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