anchor.diff:      class procedure FillVirtualFieldDefs (aFieldDefs : TmVirtualFieldDefs; const aPrefix : String);
       class function GetKeyField : String;
       function GetPropertyByFieldName(const aFieldName : String) : Variant;
  -    procedure SetPropertyByFieldName(const aFieldName: String; const aValue : Variant);
   
       property Key : TBooleanDatumKey read FKey;
     end;
  
positive.code:   Result := BoolToStr(FKey.Value, true);
  end;
  
  procedure TBooleanDatum.SetPropertyByFieldName(const aFieldName: String; const aValue: Variant);
  begin
    // none
  end;
  
  end.
  
negative.code: interface
  
  uses
    Classes,
    {$IFNDEF FPC}mInterfaces,{$ENDIF}
    mDataProviderFieldDefs, mDataProviderInterfaces, mDataProvider;
  
  type
  