TParams.CreateParam Method

Creates a new field parameter object and inserts it into the Items list.

Pascal

function CreateParam(FldType: TFieldType; const ParamName: string; ParamType: TParamType): TParam;

C++

__fastcall TParam CreateParam(TFieldType FldType, const AnsiString ParamName, TParamType ParamType);

Description

Call CreateParam to instantiate a new TParam object and add it to the Items managed by this TParams object. Specify the field type of the new parameter as the value of FldType, specify the name of the parameter as the value of ParamName, and specify the type of parameter as the value of ParamType.

Note: Parameters for datasets that represent queries are only created by specifying parameters in the SQL statement. The TParam objects in such as dataset's Params property are created automatically when parameter tokens are added to the SQL statement.

C++ Examples:

Copy Code

/*
  This example saves params from a ClientDataSet, alters them
  and restores them.
*/
TParams *SavedParams;

void __fastcall TForm1::SaveParamsClick(TObject *Sender)
{
  // Save the parameters for the TDataSet
  SavedParams->Assign(CDS->Params);
}

void __fastcall TForm1::AlterParamsClick(TObject *Sender)
{
  CDS->Params->CreateParam(ftInteger, "StateParam", ptInput);
  CDS->Params->CreateParam(ftInteger, "MyParam", ptInput);
  for (int i = 0; i < CDS->Params->Count; i++)
    if ((CDS->Params->Items[i]->IsNull) &&
       (CDS->Params->Items[i]->DataType == ftInteger))
      // Items is the default property, so you can omit its name
      CDS->Params->Items[i]->AsInteger = -1;
}

void __fastcall TForm1::RestoreParamsClick(TObject *Sender)
{
  // Restore the parameters to TDataSet
  CDS->Params->AssignValues(SavedParams);
}

#include <memory>       //for STL auto_ptr class

void __fastcall TForm1::FormCreate(TObject *Sender)
{
  // Initialize SavedParams
  static std::auto_ptr<TParams> _SavedParamsCleaner(SavedParams = new TParams());
}

Delphi Examples:

Copy Code

{
  This example saves params from a ClientDataSet, alters them
  and restores them.
}
var SavedParams: TParams;

procedure TForm1.SaveParamsClick(Sender: TObject);
begin
  { Save the parameters for the TDataSet }
  SavedParams.Assign(CDS.Params);
end;

procedure TForm1.AlterParamsClick(Sender: TObject);
var
  I : Integer;
begin
  CDS.Params.CreateParam(ftInteger, 'StateParam', ptInput);
  CDS.Params.CreateParam(ftInteger, 'MyParam', ptInput);
  for I := 0 to CDS.Params.Count - 1 do
    if (CDS.Params.Items[I].IsNull) and
       (CDS.Params.Items[I].DataType = ftInteger) then
      { Items is the default property, so you can omit its name }
      CDS.Params[I].AsInteger := -1;
end;

procedure TForm1.RestoreParamsClick(Sender: TObject);
begin
  { Restore the parameters to TDataSet }
  CDS.Params.AssignValues(SavedParams);
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  { Initialize SavedParams }
  SavedParams := TParams.Create;
end;

procedure TForm1.FormDestroy(Sender: TObject);
begin
  SavedParams.Free;
end;