TClientDataSet.FetchOnDemand Property

Indicates whether to fetch data packets from the provider on an as-needed basis.

Pascal

property FetchOnDemand: Boolean;

C++

__property Boolean FetchOnDemand;

Description

By default FetchOnDemand is true, meaning that the client dataset fetches additional packets of data as needed (for example, as a user scrolls through data, or conducts a search). If the provider does not automatically include BLOB fields or nested detail sets in data packets, setting FetchOnDemand to true causes the client dataset to fetch these values when needed as well.

Set FetchOnDemand to false only if your application contains code that explicitly fetches data packets as needed using the GetNextPacket method. Similarly, if FetchOnDemand is false and the provider does not include BLOB data by default (Options includes poFetchBlobsOnDemand), the application must fetch BLOB fields explicitly using the FetchBlobs method. If the provider does not include nested detail sets (Options includes poFetchDetailsOnDemand) and FetchOnDemand is false, the application must fetch nested details explicitly using the FetchDetails method.

Delphi Examples:

Copy Code

{
This example shows how to use the BeforeGetRecords event
handler (a TRemoteEventType value) to send the provider
information it needs for incremental data fetching. Before
fetching the next data packet, the client dataset packages
up the key value of the last record so that the provider
knows where to begin the next data packet. It also sends
some application-specific information, which is stored in
Memo1.  This method is used to pass the sql statement and the
value of the first field for the last record to the server so
that the server can return the correct records. The complete
project using this code example is in
Demos/DelphiWin32/VCLWin32/MIDAS/Pooler.
}
procedure TForm1.ClientDataSet1BeforeGetRecords(Sender: TObject; var OwnerData: OleVariant);
var
  LastValue: OleVariant;
  CDSClone: TClientDataSet;
begin
  if ClientDataSet1.Active then
  begin
    CDSClone := TClientDataSet.Create(Form1);
    try
      CDSClone.CloneCursor(ClientDataSet1, True);
      { turn off FetchOnDemand so that the clone only fetches
        the last LOCAL record }
      CDSClone.FetchOnDemand := False;
      CDSClone.Last;
      LastValue := CDSClone.Fields[0].AsString;
      CDSClone.Close;
    finally
      CDSClone.Free;
    end;
  end else
    LastValue := NULL;
  OwnerData := VarArrayOf([Memo1.Lines.Text, LastValue]);
end;

procedure TForm1.Button2Click(Sender: TObject);
begin
  ClientDataSet1.PacketRecords := StrToInt(Edit1.Text);
  ClientDataSet1.GetNextPacket;
end;