TDataSetProvider.BeforeGetRecords Event

Occurs before the provider creates a data packet and sends it to a client dataset.

Pascal

property BeforeGetRecords: TRemoteEvent;

C++

__property TRemoteEvent BeforeGetRecords;

Description

Write a BeforeGetRecords event handler to respond to custom information from a client dataset. BeforeGetRecords is part of the mechanism by which a provider and a client dataset communicate information about data fetching. When the provider is part of a stateless application server, this mechanism allows the provider and the client dataset to communicate persistent state information.

When the client dataset fetches data from the provider, the following events occur:

1.The client dataset receives a BeforeGetRecords event, where it can encode custom information into an OleVariant.

2.The provider receives a BeforeGetRecords event, where the OleVariant from the client dataset appears as the OwnerData parameter. The provider can respond to or change that information before it creates a data packet.

3.The provider generates the data packet.

4.The provider receives an AfterGetRecords event, where it can encode custom information into its OwnerData parameter or respond to information from the BeforeGetRecords event handler.

5.The client dataset receives an AfterGetRecords event, where it can respond to the custom information returned by the provider in its AfterGetRecords event handler.

Delphi Examples:

Copy Code

{
This example shows the implementation of a provider BeforeGetRecords
event handler and a RemoteDataModule UpdateRegistry method.  The
complete project using this code example is in
Demos/DelphiWin32/VCLWin32/MIDAS/Pooler.
}
procedure TPooledRDM.DataSetProvider1BeforeGetRecords(Sender: TObject;
  var OwnerData: OleVariant);
begin
  try
    Query1.Close;
    Query1.SQL.Text := OwnerData[0];
    if not VarIsNull(OwnerData[1]) and not VarIsEmpty(OwnerData[1]) then
    begin
      Query1.Open;
      if not Query1.Locate(Query1.Fields[0].FieldName, OwnerData[1], []) then
        raise Exception.Create('Record not found');
      Query1.Next;
    end;
  finally
    OwnerData := NULL;
  end;
end;